The full expression is "Fifty-four Forty or Fight." It was the campaign slogan of Presidential candidate James K. Polk in 1844. In the 1840's pioneers streaming out to the Oregon territory were all the rage, but the problem was no one was quite sure where the northern border of the territory was, and when you might actually be in Canada, which of course was a foreign country owned by the British. The U.S. position was that the northern border of the northwest corner of the United States should be 54 degrees 40 minutes north latitude, (which is actually so far north that it is now the southern border of Alaska.) As you can imagine, the British had other thoughts about this as this would have left them without any Pacific Ocean access on the west coast of North America. At one point some hotheads on both sides thought this issue could escalate into yet a third war with the British empire. James Polk campaigned on all this war fever border macho in the 1844 election, and took the campaign position we should fight Britain to establish this as the new border, complete with the new catchy slogan mentioned above. He won his election, and then dialed it down a bit as it then started to look like we were also going to be headed into a war with Mexico to establish the southern border. President Polk wisely decided he did not want to have to fight a two-border war with two different countries at the same time, and so he entered into negotiations with the British. The British proposed the 49th parallel as the new border, which among other things allowed us to have the border as a nice straight line, and so the U.S. accepted this proposal, and that is our current northern border today.
