How can I stop my armys turning into rebells????

I'm keep looseing full stack, high end armys. I click end turn and the following turn my army have become rebells.

Have high loyalty generals lead them or have a King with more influence. Or both.

What Myth said. Any stack without a leader can fall prey to corrupt and seditious tendencies. When there isn’t a leader around put the stack safely into a city.

Low loyalty commanders can be trouble too but they can be dealt with by improving their loyalty or by keeping them constantly subordinate in a stack with a better a man. They do have a useful cavalry contingent after all. In extreme cases you can always send the traitorous types on a forlorn hope where they can die with honor and dignity before they cause you any grief!

And to add some more you could have a net work of forts so that when your army travels, it camps from one fort to another. An army in forts DO NOT turn rebel, even when they don't have a general. It's just like putting them in a city. I usually keep my field armies in forts close to strategic / border cities, to avoid them getting depleted by plague :( cos it's a pain in the back side to re train them.... cos have to march back to the nearest castle :( lol