I'm very very strong but always hidden, eventually, my time will come and I'll fit in, what am I?

Question

I know I'm not welcome
But I keep coming back

Eventually I'll
Be under your attack

At a time you will choose
I will be swept away

Although ultimately
I will return some day

Keep in mind through it all
Part of me comes from you

So you'll win the battle
But the war starts anew

What am I ?

Answer 1

Bones (always hidden under your skin but when you die and your body decomposes, they will fit in with the rest of the bodies in the graves)