I need some history essay help please!?

So I have to write a essay about either the Aztec or Mayan empires. I have to write the paper about 4 before and after effects that happened when the Spanish came to invade them. Example: before the Spanish they both worshiped the sun god and were polythilistic but after the Spanish they converted to Christianity. I need more please! It would really help a lot because i have no idea what to write about!