How was Rome able to conquer and maintain its great empire?

Rome was able to maintain its empire by lenient treatment
of the peoples in conquered areas. They were not required to pay Roman taxes, and were
allowed some degree of self rule. The only requirements imposed on them were to provide
soldiers for the Roman army if needed, and not join an alliance with any other power
against Rome. The Jews in Palestine were particularly troublesome, but this was more
from a nationalist standpoint than from ill treatment by the Romans. Herod, the Roman
governor, was himself a native of the area. The Romans were also quite tolerant of
religious differences. Religion to the Romans was considered a civic duty; and the form
it took did not matter. This did prove a problem later with the Christians who denied
the Roman gods. The Empire collapsed for a number of reasons; but a major factor was
that it had grown too big. The army was spread too thin to defend its borders, and the
Empire pretty much collapsed on its own weight.