For my history summative we have to write about a controversial topic in history(obviously :P) and try and prove one side. I have absolutely no idea :(. The whatever it is that I'm arguing had to occur before the 1600's. Any interesting ideas?

There is a search engine called Google. If you enter into it some of the keywords in your question, you will get info that will help you. I found this (and several of these events lend themselves to your homework assignment):

Timeline of United States pre-history (before 1600)
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This section of the Timeline of United States history concerns events before 1600.

[edit] 1400s

* 1492 - Christopher Columbus lands on one of the Bahamas Islands, discovering the New World for 15th century Europe.
* 1497 - John Cabot lands in Newfoundland, beginning the British presence in North America.

[edit] 1500s

* 1513 - Vasco Núñez de Balboa crosses isthmus of Panama, sees Pacific Ocean.
* 1513 - Juan Ponce de León defeats Tlaxcala, a small state neighboring the Aztec empire.
* 1520s - Spanish begin conquest of Maya civilization.
* 1521 - Hernán Cortés destroys the Aztec empire.
* 1524 - Giovanni da Verrazzano, working for France, explores coastline from present-day Maine to North Carolina.
* 1542 - Hernando de Soto discovers the Mississippi River, strengthening Spanish claims to the interior of North America.
* 1565 - Admiral Pedro Menéndez de Avilés founds St. Augustine, Florida the first Spanish settlement in the New World, and is the oldest continuously occupied European settlement in the continental United States.
* 1570s - Iroquois Confederacy founded.
* 1587 - Sir Walter Raleigh founds Roanoke Colony, the first English settlement in the New World, in the Virginia Colony.
* 1590 - Roanoke Colony found deserted.

Try the year 1066 and whether William the Conqueror had a legitimate claim to the throne of England or not. Or, more generally, who DID have a legitimate claim.

I have the same question right now in my college history class. This question is difficult because you don't want to bore the crap out of everyone answering the question in a 10 page paper. Try the black plague.