Fantasy vs. Science Fiction

Friends, but why must sci-fi necessarily involve aliens? In my opinion, this is a frequently used, but by no means essential, attribute of the genre. War? Hmm... I haven't read a vast number of science fiction works (only a small number), but I've already encountered works where, on the contrary, humanity is trying to solve its own problems related to natural disasters and apply its scientific knowledge not to destroy its own kind, but to save itself. And it seems to me that the book I read is not the only one of its kind. Sci-fi often uses a time machine or something else that, in one way or another, moves people (or perhaps not only people) to another time period; sci-fi can describe an alternative reality (our time, but one aspect of people's lives is significantly changed, or some incredible scientific discovery has been made/a new weapon has been invented/.../). One could go on. For some reason, everyone immediately remembers Star Wars when they hear "science fiction." It's like equating all fantasy to The Lord of the Rings. The work is, of course, one of the best in the genre and one of the most famous... But the genre doesn't rest on The Lord of the Rings alone, does it?:)