1) That is a thesis in itself. Here's another:
The Brazilian Rainforest is a treasure to the planet and to the animals living therein, so humans should work harder to save its existence.
2) What do you want to say about WW2?
e.g., World War 2 was a violent war for the people involved abroad, as well as for the ones at home.
3) That is a thesis in itself. Here's another:
One of the most rewarding types of sports are winter sports because they help develop the body and mind.