European here. What do you mean? Employment contracts are not common or mandatory? Unheard of here. I painted my grandma's house for money and we still wrote a single page contract.
Since most states are at will employment, you don’t need a reason to fire someone, just like an employee doesn’t need a reason to quit. Both parties can end employment without cause at any time for any reason. There are some varying exceptions to this, but it’s mostly the case.
Obviously employees all (maybe almost all) have employment contracts