The battery on my cell phone died yesterday and as my family and I went to Mass I left the phone at home recharging. After Mass we visited some friends and later that evening we returned home. I turned my phone on and noticed I had a voice message. I went into my voice mail and in a male voice that is unknown to me, the only thing the message said was "You are in America, speak English" He left that message I imagine because the voice mail prompt in my phone is in Spanish, and it's in Spanish because the vast majority of people that call my personal cell phone are Hispanic and most don't speak English.
So being that I don't understand or know many of the historical things and phrases in the English language, I thought I'd ask here, why is America understood to mean the United States? Geographically America is a continent that spans from Canada all the way down to the southernmost tip of Argentina. So where does the understanding or idea that the US is America and vice versa come from?
Note: When I say I don't understand phrases here are some that just make no sense to me, although I understand the meaning behind them.
1. Pulling your leg
2. You have a chip on your shoulder
3. You have an ax to grind
4. The whole 9 yards
Disclaimer: I am not the least bit offended by the message as who I am and where I stand as a Mexican man and a US citizen is clear to me. I also mean no disrespect, but I'd really like to know and understand that idea or mentality that America = The US.

