Who is writing the background of this map?
If you look at the cities in the top two islands one is called Alberta and the other Old Quebec. There is also a city named New Quebec on the map. And cities could have been rebuilt, who knows how far into the future this is. And what it comes down to is I don't really like ruins. Did ruin a city and call it yellowstone around all the lava stuff.
And to all the critics about "have other countries around it", ala Mexico and Canada. The map is not North America. It is United States of America. It was a conscious choice to make it just the US. Feel free to make a North America map and make it accurate to current day. I will be in my future, fantasy world. I think when you play the map, or look at it in the editor, you will see some city names and other aspects that could be nods to future events, such as the volcano and ruined yellowstone.
So think of it as all the land mass around the US got destroyed conveniently along the modern day border, or suspend thy wicked disbelief and realize it is just a map that happens to have a passing resemblance to the USA but no other connection.
And the resources around the country I thought were just a good idea and a small motivation to get off the main landmass. Other that you can think of them as outposts built during the war, maybe weapons platforms that could be scrapped for their resources in our now devolved medieval like society.
I made up a story in my head with most choices I made, but some were just to make the map cool, or fun to play. Every choice is a creative one and might not match up with the story in your head, or what you want the story to be, but my map, my story.