Mexico

World War I (WWI) brought immigrants from various countries, but the most number of immigrants came from one country; and that country was Mexico.

World War I, World War II, and the Cold War

The proper noun forms for the first world war is World War 1, World War I, or World War One.

because it was the world war that ended after the first world war. Also referring to world war as a war that has most countries fighting in it.

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