It's simple. He sent a bunch of Spam back in time to the Donner party and then destroyed his time machine so that they couldn't use it to escape into the 21st century and kill people to make more Spam out of them. But his plan backfired because the surviving Donner party members passed the story down all the way to their modern-day descendants, who attempted to take over Dr. Von Stroheim's time machine because they knew he was going to destroy it, and they planned to go back and bring their ancestors into the 21st century after all so that they would finally get to satisfy their voracious cravings for human Spam, or, as they called it, "Hu-mam." But Dr. Von Stroheim knew that the Donner party descendants would know when he was going to destroy his time machine, so he went back in time and destroyed it a day earlier, and then the next day when they showed up he probably called the police but I doubt if he would be able to prove anything so the police probably let them off with a warning.