Hitler was a sworn enemy of communism. considering this, why did he make the nazi-soviet pact with stalin? why did he decide to nullify it

Because hitler wanted everyone to be equal and jews at the time weren't like him so he killed them

He wanted to keep the Soviets at bay while he went on to wage war in Western Europe and was able to do that by agreeing to split up Poland -- something none of the Western powers would think of doing. Eventually, he was going to turn against them. Hitler had long planned an attack against the Soviets and the pact was only there to buy time in the end, something that Stalin failed to see.

Ongoing civil wars western roman empire finally collapsed476 c.e. romulus, the last of theroman  emperors in  the west, was overthrown by the germanic leader odoacer, who became the first barbarian to rule in rome. the order that the  roman empire  had brought towestern  europe for 1000 years was no more.