Well, taking up arms to create a country of your own, for and by those you see as part of your own group (your nation, or whatever) - that *is* a political act. There's no way around it. And most times, setting up a new country, a new state, founded on some sort of shared bond by those who are in on the venture, isn't something that can be done in a void, on truly virginal soil. Or even with the claim that "there's a tyranny here which is known to oppress everyone in these lands, except for its own cronies - so this tyranny must be thrown out". Even in the thirteen colonies there were many people in 1776 and some time after who were not in on the idea of rebellion against the crown. Plus the slaves, most of whom presumably didn't have an opinion, and anyway they were never asked.
At best, you can make it appear to the world around that there were no viable claims to a particular part of the earth that you claim (or that one's forefathers claimed), before it was settled by the group you claim to belong to. Or that the claim that your group is making is older and more steady, has better credentials than anyone else's. Very few communities of people - nations, speakers of a certain language etc - can say truthfully: "we didn't grab our land from anyone but nature".
Of course over hundreds of years, the tide of history often mixes together people who are living in a certain patch of the earth - such as in Britain where there were Celts, Angles, Saxons, Normans and lots of others - and they might get to feel a common identity. At the time when some people is/are trying to break out of the national melting pot, it's never going to look that simple though. And very often it will be violent or disturbing.
Not saying nations or nation-forming is wrong in any way, but they are eminently political creations. It's VERY iffy to work from the line that "some people have an absolute right to nationhood and a country of their own to live in - but others simply don't, they don't qualify as real peoples".