In the world, which is the richest state in the world?

The richest state in the world is the United States.

Explanation:

Only because of the fact that the United States has the largest economy

If past history is an indication, the sirens will save hundreds of lives.

The purpose and importance of the weather sirens are already stated in the first two sentences. The last sentence discusses the advantage of its usage in proper timing. The idea in the third sentence must be restated to make it viable.