One of the causes was that the US government wanted the black hills for gold, but the Sioux refused to give up the black hills causing conflict.
There are a couple of reasons for why the empire didn't last. One of those reasons is that the empire was too great (big). Because the empire was too huge, it was divided into different parts after Alexander's death. He also didn't have an heir to the throne, so when he died, officials fought for power and to become king, which also contributed to the fall of the empire as well.
Because they’re two different countries
Christianity is a monotheistic religion that originated from Jesus who founded it. Judaism is the jewish religion made first by Abraham , then the newest of the 3 biggest religions is Islam founded by Muhammad
Please note all 3 religions worship the same god, they just have different holy texts, and views on gods prophets.