In the following sentence, which is the dependent clause?
The World War II soldier was a hero, especially because of his actions during the invasion of Normandy.

A dependent clause is a group of words with a noun and a verb. It does not express a complete thought so it is not a sentence and can't stand alone. The independent clause here is, “The World War II soldier was a hero,” since that could stand on its own as a complete thought. The rest of the sentence, separated by a comma, is a dependent clause.