There is a national teaching license in the US (or was until fairly recently, haven't checked the last few years), in addition to the individual state licenses and (iirc) the national cert could only be done after one has been teaching in their home state for awhile (an add-on to the state certain). Certain states did not support the national cert. back during the teacher shortage for obviously reasons. The good old days- now districts can be choosy even if they are hiring. Now many are not replacing teachers, merely spreading the kids over the existing faculty. (IMO best time to teach is when there's a shortage - former high school science teacher and interview committee member before the military reactivated me for 9/11, ... I was looking at the national cert myself years ago).
Most state teaching certs can carry over to other states but some do not; there's a database available thru district personnel offices, maybe online which tell you if your teaching cert carries over based on where you earn it (if not on the list -then no for that state). Getting a little off topic but another problem is my prime hiking month is May yet most American high schools do not get out until the end of May : ( So after the military, I took a position not quite as stable but pays better (at least last year)-- and now May is my vacation month (woohoo!!!). Back to work in June/July but that's broiling time/thunderstorm time around here, so, meh...
(ed: grammar, add)