How do you combine all troups?
 

There are several situations in which I will end up with two stacks. I want to combine the two stacks into one. However, when I click on the stack and get the (<->) thingy that allows me to merge them I can make at best two stacks of 1 and n-1 and then dismiss the one. I cannot find a way to make 0 and N which is what I almost always want (this is also true when moving from reserve to stack).

after you select the first stack of the 2 you want to merge, do not click on the double arrow button that appears below, instead just click on the portrait of the second stack, also make sure the total troops available is not more than the maximum allowed by your leadership.

Ok thanks. I'll give that a try.