Is there historical evidence that even countries/states that trust each other sometimes go against each other?

Question

I am doing a paper on why countries find it difficult to always fully cooperate in the international world, and want to show example of a country/state that another country/state trusted that still did not cooperate at one point, and went against each other.

Answer 1

i'v heard that george washington wanted to invade canada....

Answer 2

Politics, energy policies,

America has gone to many a countries resque in their hour of need. Then when we ask for their support to help another country they go french on us. Just look at the last 100 years of war and our ALLIES sic.
How about all the countries that trusted Hitler, including PM Chamberlan. Good thing Winston Churchill had the guts to call it like he saw it. Hitler talked his way into many counties then took them over.

Answer 3

Just google 'civil war'.

You'll find plenty of examples.

Answer 4

VIKINGS