if alliens where really monitoring or visiting us some things would had happen already for sure.
first
we would be their slaves in the best case and their food in the worst (something like a cattle to them).
like cows are to us or at the best case like monkeys are to us (for experiments etc).
alliens might exist but its really impossible to had come and visit us here ,
now about ufo's they are very real but think about this.
they could be secret technology of today or ancient really secret technology.
plato mention atlantis on his writings ...
our history anyways is sure not this one they teaching at schools...
its much older and much more advanced...
the proofs of that is the parthenon in athens greece and the pyramids in egypt two buildings we cant rebuild today not even copy them with our 'superior advanced" technology.