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Why did Britain and France declared war on Germany over the invasion of Poland, but not the USSR?

Sarah Jenkins
Sarah Jenkins
Lead Content Curator · Mar 30, 2026 · Updated Apr 13, 2026

They were already at war with Germany when Germany invaded the USSR. If you were asking why the USSR didn't declare war on Germany, then it's because of the [Molotov-Ribbentrop pact](_URL_0_). The Germans violated that pact when they invaded the USSR in 1941.

43
Words

1 min
Read Time

#341
of 500 in History

-40%
vs Category Avg

The Short Answer

They were already at war with Germany when Germany invaded the USSR. If you were asking why the USSR didn't declare war on Germany, then it's because of the [Molotov-Ribbentrop pact](_URL_0_). The Germans violated that pact when they invaded the USSR in 1941.

Analysis

Key Concepts: Germany, ussr, invaded

This explanation focuses on germany, ussr, invaded and spans 43 words across 3 sentences. At 40% below the average History explanation (72 words), the answer takes a direct, no-frills approach — sometimes the simplest explanation is the most effective.

What This Answer Covers

The explanation opens with: “They were already at war with Germany when Germany invaded the USSR.” It then elaborates by explaining the root cause, ultimately building toward a complete picture across 3 connected points.

How This Compares in History

Ranked #341 of 500 History questions by answer depth (top 69%). This is in the concise tier — a focused explanation that prioritizes clarity over exhaustiveness. Many readers prefer this level of directness.

Frequently Asked Questions

Is there a simple explanation for why britain and france declared war on germany over the invasion of poland, but not the ussr?

They were already at war with Germany when Germany invaded the USSR. If you were asking why the USSR didn't declare war on Germany, then it's because of the [Molotov-Ribbentrop pact](_URL_0_). The Germans violated that pact when they invaded the…

How detailed is this explanation compared to similar History questions?

This is a focused answer at 43 words, ranked #341 of 500 History questions by depth. The key concepts covered are germany, ussr, invaded.

What approach does this answer take to explain britain and france declared war on germany over the invasion?

The explanation uses root cause analysis across 43 words. It is categorized under History and addresses the question through 1 analytical lens.