how to summon faster?

So I am still new to the game, and I’m wondering, how do I summon faster? (make that blue bar during raid increase faster?)… Does it just increase as I level naturally? Or do I have to upgrade something… Thanks !

Leadership is the stat that increases the blue bar and allows you to summon more troops at a faster rate. You can gain leadership by simply leveling up or equipping new hero gear that has more leadership than your current hero gear.

Thank you!