It's Not about War nor Politics (spoilers)

That's the reason why the political divisions are purposely muddled. There are a few themes from the director/writer Alex Garland:

1.
President is a fascist dictator. His political party is irrelevant. He has betrayed the Constitution and has sent the U.S. military to kill citizens which harms all of us and destroys our country.

2.
The political alliances (ex. California & Texas) don't make sense because they're not important.

Unity over political partisanship in the face of a fascist government is important. Country over party.

3.
There is a warning about our political divisions. Fascist leaders exploit and deepen divisions to gain and maintain power. A democracy needs compromise and cooperation to survive.

"Every time I survived a war zone, I thought I was sending a warning home. 'Don't do this.' But here we are."

4.
The movie is from the point of view of journalists, the 4th pillar of democracy. They are there to record the events while remaining completely impartial. Their values and experiences are part of the main focus. It's not an accident that the president has forbidden all journalists in D.C. since tyrants fear the truth, criticism and exposure.

This movie is a tribute to the war photojournalists who risk their lives to bring us information and images.