What am I?

I can start a war or end one
I can give you the strength of heroes
Or leave you powerless
I might be snired with a glance
But no force can compele to stay
What am I?
                       -Riddle man-
I've moved mountains.
I've sailed the seven.
Many long to have me,
Yet many cannot keep me.
Some have dug mountains with needles,
Others have emptied oceans with teaspoons.
All in my name.
What am I?

I've sank cities.
I've walked bare foot on burning fires.
I'm the bridge between Heaven and Earth.
I connect women and man.
I'm the difference between black and white.
I'm the best of both worlds.
Kings have relinquished thrones for me.
Peasants have turned into kings because of I'm.
I'm the best of mankind,
But I can also be the downfall of mankind.
What am I?

I'm not visible,
 but you wish to see me.
I'm not tangeble,
But you wish to hold on to me.
I've given you sleepless nights,
And I've given you reason to smile.
I've broken your heart
And I'm the only one who has the power to mend your heart.
The answer lies in your heart.
What am I?