Naw, there are higher records in all three cases.

An example for the first (though cruelty is hard to measure objectively):

https://en.wikipedia.org/wiki/Atrocities_in_the_Congo_Free_State

For the second:

https://en.wikipedia.org/wiki/Mongol_Empire

Here’s a list of the third, admittedly debatable which supersede the US depending on when you define each individual beginning of the end and end of the end, but you’ll find at least one that suits you if you’re being honest:

https://go2tutors.com/16-nations-that-rose-to-power-then-collapsed-almost-instantly/