What led to the conflict between persia and the greeks? answer?

Idon't really understand the question. it counts for 20% of my lesson grade and i really need putting the answer into words. anything will . i need asap so im awarding 30 points.a disagreement between states of the united states concerning the rights of states vs. the authority of the national government led to the civil war. state governments were forced by war into a subservient position. what might happen if national governments ceded their authority to a world government by international treaty?

The quest for wealth or was a major factor contributing to the age of exploration? grants god gold glory

:) during the cold war, people were afraid of communists, both outside and inside the united states. the red scare and mccarthyism that grew out of these fears were damaging to the american way of life. during the mccarthy years, many of the freedoms guaranteed in the bill of rights were limited. write a paragraph explaining what lessons can be learned from the mccarthy era about what u.s. citizens need to protect in order to preserve the democratic political system and the american way of life.