Your history teacher is, simply, wrong. The swastika and related symbols are widespread in Eurasian and North American cultures as symbols of protection and good fortune. They gather strength from the four directions and from the clockwise/sunwise direction of the sun as seen in the northern hemisphere. The participants in the folk cultures that used these symbols would never have explained the traditional symbol with the sort of dogmatic interpretation that says, "see how these bars are above the lower bars; that means 'peace by oppression'." That is simply nuts. The folk would say, "oh that's for good luck," or, "oh, that's to help protect the animals in the barn. I'm not sure why, but we've always used that."