Companies have submitted their bids for the wall President Trump wants to build on the U.S-Mexico border, one of the causes of strained relations between the two countries recently.

At the same time, Phoenix has opened a second trade office in Mexico, and that country continues to be Arizona’s top trading partner.

So, what is the history of America’s relationship with its southern neighbor?

Veronica Martinez-Matsuda is historian at the Industrial Labor Relations School at Cornell University.

How much of this relationship is based on what’s going on now, and how much of our interaction is based on history?