What united the various Indian states and regions? overseas exploration

a single encompassing
philosophy

trade

a common religion

i think the answer is b.

polisit can also mean a body of citizens. in modern historiography, polis is normally used to indicate the ancient greek city-states, like classical athens and its contemporaries, and thus is often translated as "city-state". the body of citizens came to be the most important meaning of the term polis in ancient greece.

using the media to encourage public support for an idea.

encouraging congress to take action

establishing a public policy goal for the nation