Countries don’t exist in vacuums. A big part of geopolitics is figuring out how to manage not getting attacked while being able to build up things other than war machines. For instance, if you have allies you trust, your COMBINED force projection would need to be enough to prevent attacks, leaving each with more room to focus on their economies. If you want to be completely isolated, sure, you have to be able to individually defend yourself, but we live in a world where we really CAN’T be completely isolated, so it only makes sense to try to work together.
Countries don’t exist in vacuums. A big part of geopolitics is figuring out how to manage not getting attacked while being able to build up things other than war machines. For instance, if you have allies you trust, your COMBINED force projection would need to be enough to prevent attacks, leaving each with more room to focus on their economies. If you want to be completely isolated, sure, you have to be able to individually defend yourself, but we live in a world where we really CAN’T be completely isolated, so it only makes sense to try to work together.