Wasanelder Once,
Do you think there are any other reasons you would be willing to use force outside of someone breaking into your house to harm you and your family?
For example, if you saw a women being raped would you attempt to stop the attacker? If you were unable to stop the attacker by yourself, would you get a group of people together to stop the attacker?
If you said yes to these - then you understand the principles of warfare.
We don't just fight wars in response to large scale attacks on our own persons or property. The US has fought wars for many reasons. Like stopping the genocide that was going on in Kosovo. Like stopping the Taliban from ruling and running terrorist operations out of Afghanistan. Or to protect a sovereign country from the invasion by it's neighbor Iraq.
Imagine if we had not fought Korean war. That too was called a "goalless battle with no purpose or end in sight". The entire Korean peninsula would now be under the control of the madman Kim Jong Un. Instead of Seoul being a city filled with prosperity and social freedoms it would instead be home to a population of starving and freedomless men, women, and children.
Imagine an Iraq still under the brutal mandates of Saddam Huessien? Or even worse - his sons!
There are many reasons we fight wars. A country doesn't have to bomb Pearl Harbor of fly planes into the Twin Towers for us to find force a necessary evil to stop an even greater injustice.