I don't think it's that simple. Leaders are chosen as representatives of the country. So when a country goes to war, it's usually in the best interest of that country. And whatever is best for your country is usually best for you.
If North Korea threatened to launch a missile on the United States, first of all, the people in North Korea can't just be like, "We're not fighting this war." Cuz 1) A lot of them are already brainwashed and believe the war is the right thing. 2) even if they didn't want to, they would be put to death or would die revolting for their country. A civil war would break out within their own country. War is inevitable during times of irrational conflict.
And then if you're in the United States and you volunteered to be in the army or whatever, you have to go because it's required by law. On top of that, you'd want to go because dying for your country is what you believe in. It's a country of freedom, and the United States can't be free it decides to just walk away from the fight. The nuclear missile is coming no matter what. It doesn't have to be a nuclear missile, it could be anything really.
Also, the Czech Republic, in my opinion, is not really a country to get into wars because it doesn't have a prominence in the world. It doesn't have a lot of power, so even if it had a leader that wanted to go to war, the country wouldn't get very far, so it's in its best interest to avoid wars. Which makes sense. Weak people avoid fights and conflicts because they know they'll lose. Strong people avoid fights or conflicts because they believe that's the best course of action at the moment.
And on the flip side, there's not much of a benefit when you war against the Czech republic. There's nothing to "own" or gain from that country. Maybe there is, I don't know honestly. If you war against the United States and win against the United States, then there's definitely something to won there. If you defeat the United States, then your country would become the world power and have some influence in the world.
Also, Abby, no matter where you go there will always be conflicts. These conflicts can usually be settled in a debate or rational discussion, but what happens when the other person refuses to? You have no choice but to fight them. You can't just walk away and be a pacifist your entire life. Maybe you could, but people who don't get into conflicts are weak, walked over, and stand for nothing of value.
War is necessary.