In fact there is no “declare all battles and move in” stated in the rulebook(s). That idea might be the reason for your misinterpretation.
In the Combat Movement Phase, in principle (to keep it simple and not to list exceptions), you move all units that end their movements in hostile territories:
@rulebook:
During the Combat Move phase, all movement must end in a hostile space, with a few exceptions (see below).
…
or
@rulebook:
In this phase, you may move as many of your units into as many hostile territories and sea zones as you wish.
That’s it! Then this phase is over.
If the units that were moved in the Combat Movement Phase meet enemy units in the hostile territories, then combat will occur in the next phase, that is the Conduct Combat Phase:
@rulebook:
In this phase, you conduct combat against opposing units using the following sequence:
…
or very explicit in
In this phase, you resolve combat in each space that
contains units from opposing sides.
Complete all combat moves
before resolving any combat. (An
exception is an amphibious
assault, in which sea combat must
be handled before land combat.
See Special Combats on page 19.)
HTH :-)