Commander, 

Recently it was added "association activity". So if your association's activity drops below 60%, a countdown is triggered and your association is removed unless you raise the bar.

This could explain your situation

Yes, but if I do not go to the game for more than a month. But it was not.

It’s not enough for you to be active, if other members don’t connect, it lowers the percentage. And the more they remain inactive, the more it’s penalizing.

The solution would have been to remove the most innactive or/and recruit new active players. 

Hello, Sir. Does the reason for your Combine disbanding become clearer for you now? 

You can also read more about the Combine Activity here: https://plarium.com/forum/en/soldiers-inc/news-and-announcements/68910_new-feature---combine-activity-/