War : World War II (1939–1945) Chapter 01. The Pre-War System

World War II (1939–1945) — Part 1: The Pre-War System

Conflict Snapshot

Core dates (global war): 1 September 1939 (Germany invades Poland) to 2 September 1945 (Japan signs the Instrument of Surrender).
Alternative start-date convention (Asia-Pacific): many historians treat the Second Sino-Japanese War (full-scale from July 1937) as the beginning of a wider “World War II in Asia,” preceding September 1939 in Europe.
Type: Predominantly interstate coalition war fought on multiple continents; within it were also civil wars, occupation conflicts, resistance campaigns, and mass political violence (often treated as distinct but overlapping phenomena in the scholarship).
Primary coalitions (simplified):
- Axis core: Germany, Italy, Japan (formal alignments evolved over time).
- Allied core: United Kingdom and Commonwealth, France (1939–40; Free France thereafter), Soviet Union (from June 1941), United States (from December 1941), Republic of China (at war with Japan from 1937).
Outcome label (high-level): Allied victory; Axis defeat—European war terminated by German unconditional surrender in May 1945; global war terminated by Japan’s surrender in September 1945.
Deaths (range; why it differs):
- ~40–50 million deaths in one widely cited synthesis (definitionally “war deaths,” with many attribution challenges).
- Other official/compiled summaries present higher totals by counting civilian deaths more expansively and/or incorporating broader categories (including deaths from occupation policies, mass atrocities, and indirect mortality). For example, one U.S. compilation summarizes ~15 million military battle deaths plus tens of millions of civilian deaths (definitions and country coverage vary by compilation).
- Why the spread persists: inconsistent country-level record quality (especially in parts of Eastern Europe and China), definitional differences (direct violence vs famine/disease-related mortality), and whether mass atrocity deaths are tabulated inside “war deaths” or as separate categories.
Displacement (indicative ranges; why it differs): tens of millions displaced across Europe and Asia in the course of the war and its aftermath; one frequently cited postwar figure is ~11 million “displaced persons” in Europe at war’s end, but totals vary depending on whether forced laborers, POWs, refugees, deportees, and postwar border changes are counted together.
Last updated: 16 January 2026.

Milestone Timeline (system-to-war, 1919–1945)

28 Jun 1919: Treaty of Versailles signed (post–World War I settlement framework).
10 Jan 1920: League of Nations begins operating; the U.S. does not join.
Oct 1929: Great Depression begins, becoming a prolonged global downturn.
18 Sep 1931: Mukden Incident; Japan seizes Mukden and then occupies Manchuria; Manchukuo established (1932).
Oct 1935: Italy invades Ethiopia; League sanctions prove limited.
7 Mar 1936: Germany remilitarizes the Rhineland in violation of key postwar constraints.
7 Jul 1937: Marco Polo Bridge Incident; full-scale Sino-Japanese war follows (Asia-Pacific escalation).
12–13 Mar 1938: Anschluss (Germany annexes Austria).
29–30 Sep 1938: Munich Agreement; Sudetenland ceded to Germany.
23 Aug 1939: German–Soviet Nonaggression Pact signed.
1 Sep 1939: Germany invades Poland; Britain and France declare war (European war begins).
7 May 1945: German unconditional surrender signed at Reims (European war termination process).
2 Sep 1945: Japan signs the Instrument of Surrender (formal end of WWII).

1) The Post–World War I Order: Treaties, Borders, and an Incomplete Security Architecture

FACTS (institutional baseline)

After 1918, Europe’s political settlement rested on a package of treaties associated with the Paris Peace Conference, with the Treaty of Versailles the most prominent in the German case. It reshaped borders, addressed reparations, and embedded a new international organization—the League of Nations—in the aspiration that disputes would be managed collectively rather than by great-power war.

However, key pillars of enforcement were weak or inconsistent from early on. A central structural fact is that the United States never became a League member, despite President Wilson’s association with the League’s concept. This mattered because the League’s credibility and coercive capacity depended heavily on major-power coordination and willingness to impose costs (sanctions, or ultimately military measures) on aggressors.

INTERPRETATIONS (what historians argue, with attribution)

Versailles as a destabilizing settlement (Medium confidence): Many accounts stress that the postwar settlement created durable grievances and revisionist agendas, but the degree to which Versailles “caused” World War II is debated—partly because interwar outcomes also depended on domestic politics, economic shocks, and later strategic choices. A broad synthetic framing in Britannica emphasizes how the 1930s crisis saw interwar structures collapse under depression and revisionist challenges.
International order as “incomplete” rather than simply “failed” (High confidence): A more structural reading holds that the system lacked the institutional and political prerequisites for consistent collective security (credible commitments, stable coalitions, enforceable sanctions). The U.S. absence and the uneven engagement of other great powers are core elements of this interpretation.

2) Economic and Political Stress: The Great Depression as a System Shock

FACTS (economic constraints that shaped state behavior)

The Great Depression, conventionally dated from 1929, was a severe, global downturn that destabilized economies and domestic politics across regions. Governments responded in varied ways—trade restrictions, currency measures, public-works programs, and (in some cases) intensified state direction of industry. Regardless of policy mix, the depression era materially constrained budgets, affected social stability, and shaped political coalitions inside many states.

INTERPRETATIONS (links to war risk)

A cautious, evidence-aligned synthesis is that the Depression increased the salience of economic security (access to markets, raw materials, and employment) and intensified political polarization in several societies. A widely used overview of the era in international relations frames the Depression as accelerating the breakdown of interwar economic and diplomatic structures, contributing to a context in which revisionist policies by Japan, Italy, and Germany encountered weakened collective responses.

(Important caveat: economic shock is best treated as a contextual amplifier rather than a standalone “cause,” because states facing similar economic conditions made different strategic choices.)

3) Revisionism, Empire, and Competing “Orders” in Europe and Asia

FACTS (stated programs and strategic agendas, by region)

Germany (Nazi regime from 1933):
Open-source documentary records and curated reference works emphasize that Nazi ideology included territorial ambition. For example, the U.S. Holocaust Memorial Museum summarizes that the Nazi Party’s platform laid claim to territory of neighboring states and prioritized German dominance. A related concept, Lebensraum, is described in Britannica as a Nazi policy of expanding eastward to secure land and resources (with catastrophic implications for targeted populations).

Italy (Fascist regime):
Italy’s invasion of Ethiopia in 1935 is a key indicator of imperial revisionism in Africa and a stress test for League enforcement.

Japan (imperial state, Asia-Pacific):
Japan’s military expansion in Northeast Asia is illustrated by the Mukden Incident (1931) and the subsequent occupation of Manchuria and establishment of Manchukuo. From 1937, the conflict in China escalated sharply after the Marco Polo Bridge Incident, which Britannica treats as the spark for full-scale hostilities.
A later wartime ideological framing—useful here as an indicator of proclaimed regional order—was the Greater East Asia Co-Prosperity Sphere, described by Britannica as a Japan-led, self-sufficient bloc in the Asia-Pacific under Japanese control.

Status quo and security-seeking powers:
Britain and France remained central to European deterrence but carried domestic and imperial constraints. The Soviet Union’s security position evolved in the 1930s and culminated (immediately prewar) in the German–Soviet Nonaggression Pact (23 Aug 1939). The United States was a major economic power but was not committed to collective security through the League framework.

INTERPRETATIONS (how scholars conceptualize “roots” of the war)

Richard Overy (in a widely used academic text) argues that the conflict’s origins cannot be reduced to a single leader or country; he frames the war’s roots in part around the decline of older empires and the rise of ambitious powers (Germany, Italy, Japan) seeking their own imperial domains. This interpretation is best read as a macro-structural account—useful for system analysis, but not a substitute for decision-level explanations (which Part 2 will address).

4) Collective Security Under Strain: Enforcement Failures and Strategic “Buying Time”

FACTS (sequence of challenges to the interwar security regime)

The League system faced repeated crises where condemnation and sanctions did not reliably deter further action:

In Asia, the Mukden Incident and subsequent occupation of Manchuria exposed limits of collective response. Britannica notes that many observers regarded the incident as contrived by elements of the Japanese army, underscoring the contested nature of immediate causation narratives even when the broader sequence is clear.
In Africa, Italy’s 1935 invasion of Ethiopia drew international reaction but did not produce an outcome that restored Ethiopia’s position before the invasion.
In Europe, Germany’s remilitarization of the Rhineland (7 Mar 1936) directly challenged key post–World War I constraints.
The Munich Agreement (Sep 1938)—accepting German annexation of the Sudetenland—was a major diplomatic turning point that redefined deterrence expectations in Europe.

INTERPRETATIONS (appeasement as strategy vs error)

The policy commonly labeled appeasement is defined in Britannica as negotiating concessions to prevent war, associated especially with Britain’s approach toward Fascist Italy and Nazi Germany in the 1930s. The Imperial War Museums adds that appeasement was popular and perceived as pragmatic at the time, even though it is “widely discredited” in much postwar memory.

In the scholarship, two non-identical interpretations often appear:

Appeasement as “buying time” under constraint (Medium confidence): emphasizes air-defense fears, rearmament timelines, fiscal limits, and public reluctance for war (especially after 1914–18).
Appeasement as a bargaining failure that increased aggressor expectations (Medium–High confidence): emphasizes signaling effects and how successive concessions did not stabilize demands. A prominent academic treatment (Levy, 2008) analyzes “wishful thinking” dynamics and the assumption of limited aims.

This series will treat appeasement neither as a moral category nor as a single-variable explanation, but as a policy family shaped by constraints, expectations, and incomplete information.

5) Capabilities and Constraints: Technology, Mobilization Potential, and Geography

FACTS (what mattered structurally, without overclaiming)

By the late 1930s, major powers possessed (or were developing) the industrial capacity for high-intensity war—large standing armies, mechanized forces, strategic air power, and naval forces capable of long-range operations. The practical implication for the “pre-war system” is that deterrence increasingly depended on credible mobilization and coalition coordination, not simply on treaty promises.

A core geographic constraint is that WWII was not one contiguous battlefield but an aggregation of theaters—Europe (West/East), North Africa/Mediterranean, the Atlantic, China, Southeast Asia, and the Pacific—each with distinct logistics and coalition politics. This widened the gap between formal alliances and operational coordination.

INTERPRETATIONS (total war framing)

The “total war” characterization—states mobilizing large shares of economic and social capacity—is common in major syntheses (e.g., Cambridge’s multivolume history frames the war through fighting, politics/ideology, and total-war economy/society lenses). This is an analytical frame (useful for understanding why the war’s scale was so destructive), but it does not itself explain why war began when it did.

What is well-established vs. what is disputed

Well-established (high confidence)

The interwar settlement combined new borders, reparations disputes, and a League-based collective security aspiration, with the U.S. outside the League.
The Great Depression was a major global shock that undermined economic and political stability.
A sequence of major crises—Manchuria (1931), Ethiopia (1935), Rhineland (1936), China (1937), Austria (1938), Munich (1938), Nazi–Soviet pact (1939)—eroded deterrence and reshaped expectations.

Disputed / debated (medium confidence unless noted)

“Start date” of WWII: September 1939 vs July 1937 (or even 1931) depends on whether one defines WWII as a formally global war or as a connected escalation across theaters.
Relative weight of Versailles grievances vs. 1930s decision-making: scholars disagree on whether Versailles should be treated as a primary driver or a permissive condition.
Appeasement: whether it was primarily misjudgment, strategic delay, domestic-politics driven, or some combination varies across interpretations and evidence emphasis.
Casualty totals: wide ranges persist due to definitional and data-coverage differences, especially regarding indirect mortality and wartime/postwar boundary conditions.

Key Sources Used

U.S. National Archives (NARA), Surrender of Germany (1945).
U.S. National Archives (NARA), Surrender of Japan (1945).
Encyclopaedia Britannica, Casualties of World War II (deaths/displacement synthesis).
U.S. Department of State (Office of the Historian), The League of Nations, 1920 (U.S. non-membership and context).
Encyclopaedia Britannica, Mukden Incident; Italy–Ethiopia; Munich Agreement; Anschluss; German–Soviet Nonaggression Pact; Rhineland/remilitarization context (event anchors).
USHMM, Nazi Party Platform (stated ideological-political claims).
Routledge (Richard Overy), The Origins of the Second World War (macro-structural interpretation).
Imperial War Museums (IWM), appeasement background and Europe to war explainers (policy framing and public context).
Levy (2008), “Wishful Thinking or Buying Time?” (academic analysis of appeasement assumptions).
Cambridge University Press, The Cambridge History of the Second World War (major scholarly synthesis framework).

Open Questions / Uncertainties (to track in Parts 2–5)

Linkage vs simultaneity: to what extent should European and Asian escalations be treated as a single bargaining system before 1941, versus parallel regional wars that later merged? (Confidence: Medium)
Deterrence counterfactuals: would stronger League enforcement in 1931 or 1935 have materially changed later European decisions, or merely shifted timing and coalition alignments? (Confidence: Low–Medium)
Appeasement’s internal logic: how to weigh domestic political economy, intelligence estimates, and rearmament timelines against diplomatic misperception in explaining British/French strategy. (Confidence: Medium)
Boundary conditions for casualty accounting: which mortality categories (famine, disease, postwar expulsions) are methodologically defensible inside “WWII deaths” for a public-facing series, without overstating precision. (Confidence: High that uncertainty is irreducible; Medium on best public-facing range choice)