Things pre-1800 wars can help post-1800 wars

This may be better in the chat forum, feel free to move.

So, the premise is- we see from Alexander to Genghis Khan to the European colonialism that nations (and individuals) can make a huge change by conquering lands and nations. But when we get to Napoleon, if someone, a nation, (or a small group of nations) try to make a big difference there becomes a world coalition that will stop drastic changes. Any reason other than more globalism made alliances easier?
 
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