The leaders of the US, USSR, and Great Britain said they wanted to cooperate, so why were negotiations at the Yalta and Potsdam conferences so difficult?

The leaders were not honest about their goals.

Each country had its own agenda about the post-war world.
Germany and Japan were still seen as a threat by the Allies.

The end of the war was still far away.
The leaders of the US, USSR, and Great Britain said they wanted to cooperate, so why were negotiations at the Yalta and Potsdam conferences so difficult?

The leaders were not honest about their goals.

Each country had its own agenda about the post-war world.
Germany and Japan were still seen as a threat by the Allies.

The end of the war was still far away.