This thread is a top hit for searches such as "stop safari from opening old pages" on DuckDuckGo and"how to stop safari reopening in last page" in Bing. I noticed the solution to my problem was not listed here, so I am adding this reply.
My problem: I was searching for a Sega Saturn ROM for OpenEmu. I was unaware how shady such web sites catering to this market segment are. One site completely took over Safari. I could not adjust Safari preferences. I could not move off the adware scam tabs. I could not close the popup dialogs. I could not switch to a new window. Every time I opened Safari, it reopened the adware infected site.
The way to open Safari without opening your previous web pages is to hold the shift key while clicking the Safari icon. After that, I regained control of Safari. It started at my Top Sites pages. I could adjust Safari preferences and clear my history of the unwanted scam web sites.