What was the magna carta, and how was it the first step in a democratic from of government in england

 Magna Carta
Book by John, King of England and Stephen Langton. 

Ironically, the Magna Carta would inspire American colonists a few hundred years later to declare independence from the British themselves. Around one-third of the provisions in the United States’ Bill of Rights draw from the Magna Carta, particularly from its 39th clause: “No freeman shall be taken, imprisoned, disseised, outlawed, banished, or in any way destroyed, nor will we proceed against or prosecute him, except by the lawful judgment of his peers and by the law of the land.”

here is a website were you can read more about it 
www.history.com/news/ask-history/what-is-the-magna-carta

From mexican american war , us gained new mexico.