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2. CLICK the picture (and video)
3. TRY this:
Q1: Why did the war in Europe become a world war?

[Answer]

Many of the countries of Europe were empires with colonies scattered across the world.

So, when Europe went to war, it automatically meant that their colonies went to war, too.

This is what made it into the first World War. For example, the Germans (who owned part of East Africa) invaded British Uganda and the British moved from South Africa into German South West Africa (now Namibia).