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But on my side of the pond we do the invading...
This is an incredibly naïve opinion.
OP, in a perfect world, we'd have no wars and everyone would be happy and peaceful.  But we don't live in a perfect world.  Assholes come and go to war, and the rest of us have to deal with it and fight in it.  We've seen plenty of people with similar thoughts to yours come and go and they've never changed the minds of the masses.  
Wars will continue.  People, with or without children, will fight in them.  That is not going to change anytime soon.  Sadly, I only see that increasing over the next few decades. >

The day every man decides to lay down his arms there will be peace.
Until then governments will manipulate them. >

People fought before governments existed. Theirs always going to be predators that prey on good people those good people need to be ready to fight >

Self defense is not invasion. Crimes of passion are not war. 
What we have now is fabricated. Its a system we cling to out of fear and so givernments will never let go. Their need for power, control and self preservation is what modern conflicts are.
Often my nation and our allies are the ones invading, taking on much smaller nations that cannot hope to fight back. We are the violent predators, so perhaps we should choose as individuals to lay down our arms and not participate in war.
I also think the PTSD from the last conflict is creating new violence this conflict. All started when the ptsd from the conflict before that became leaders. Hitler, Stalin, Mao and Putin were all involved in the war of the previous generation and caused mass violence in their own. I think maybe we should stop making new generations of terrorists and cracked out leaders. >

If everyone took this perspective, nobody would serve/fight. >

You say that like it’s a bad thing. >

This will never happen. People will always fight. You need people willing to fight (even fathers and mothers) to fight tyranny. >

i never said it will happen eventually. i said that if it could happen, it wouldn’t be a bad thing. >

I think literally everyone ever agrees with that. >

Getting invaded usually isn't very good for children