I set up a new blog without any intention of doing redirects.
After this, I also set up a new Page for wordpress.
This page automatically showed on main page.
When I deleted it, the main page gave me the "Can not be displayed" error.
Only then I understood that whenever I click the main /domain I get redirected to the /domain/page instead.
I tried changing themes, but apparently this is not a theme issue.
WordPress has misunderstood something and always wants to redirect from my index page to the page I made before.
How do I fix this?