Because most countries involved in the war had alliances with others. And when one was attacked the ally came to protect the other. Therefore countries became more and more involved in the war
No
they’re NUCLEAR weapons
firing them at each country would cause massive devastation, literally wiping out millions of people
The principle of superposition states that the oldest sedimentary rock units are at the bottom, and the youngest are at the top. Based on this, layer C is oldest, followed by B and A. So the full sequence of events is as follows: Layer C formed.
The mongols were positive in the history