Why can't God just put a stop to evil?

In youth group, Willie has been asking us challenging questions and this was the last one that really made me think. I sat there and thought, but God DOES have the ability to put a stop to evil.

God has stopped evil before.

He flooded the earth to wipe out evil in Noah's day.

He destroyed the cities of Sodom and Gomorrah. "Then the Lord rained brimstone and fire on Sodom and Gomorrah, from the Lord out of the heavens" Genesis 19:24. "Turning the cities of Sodom and Gomorrah into ashes, condemned them to destruction, making them an example to those who afterward would live ungodly" II Peter 2:6

He sent Jesus to die for us so we wouldn't have to suffer for our own wickedness.

And if you read more history in the Bible, you will see other examples of God stopping evil. However, God doesn't always stop evil from happening. In most cases, he allows it.

Earthquakes happen. Tornadoes happen. Flooding happens. Tsunamis, volcano eruptions, war and terrorism all happen. It is all part of God's plan.

I guess the reason he doesn't just put a stop to evil all the time is because God sees the big picture. God has already seen the end. He knows how things are going to turn out. Being human, we don't see the picture God sees. We focus on the little things that happen. One person dies and we think, why did God allow this to happen? What we don't realize is that this is all part of God's plan.

God has already seen the end. Everything is working for his perfect plan.
God has already won.

I sat there and thought more about that. God has already won. Why are we so worried? Why do we try to figure everything out on our own? God already knows. Jeremiah 29:11 says that God has a perfect plan for us. I guess sometimes I forget that God already knows how everything will play out. He allows certain things to happen because he knows that in the end, it will be used to glorify Him. It may not make sense to us right now, but it will when that time comes.
I'm rambling a lot. I've been thinking a lot about how everything that happens is for the glory of God, no matter how crappy it seems at the time, because in the end God wins. How awesome is that?