How does the system of checks and balances in the federal government work?

The system of checks and balances is used to keep the government from getting too powerful in one branch.

for example, the president may veto a law passed by Congress. Congress can override that veto with a vote of two-thirds of both houses. another example is that the Supreme Court may check Congress by declaring a law unconstitutional. The power is balanced by the fact that members of the Supreme Court are appointed by the president. 

Read more on -

uncle sam would be tossing and turning in his grave : *)

a. poison gas was sprayed over battlefields by airplanes to weaken enemy positions before major attacks.