Nations have interests which come first

The Vietnam War is an easy example of this because United States intervened not to protect democracy and liberalism

But to stop the spread of communism in Asia due to the domino theory that if one nation goes communist the nations around it will also go communist

Keep in mind within a rapid span of time most of Europe when communist, China and communist and there was a massive fear that

More Nations would go communist

Hence the USA going into Vietnam military

For Europe I would argue from 1495 until the end of world War 2 the great powers of Europe

We're trying to unite Europe into one state which could be like unto China's warning States period

In the 18th and 19th centuries there was a balance of power between the power of Germany/Prussia, France, Russia, Austria and the British

Buy The turn of the 20th century Germany became strong enough to dominate the other states of Europe which play a part

For the causes of two world wars