I figured out that if there are more than 1,000 navy weapons on a carrier, the carrier will not move. After I bought extra carriers, I could move my navy.
However, this problem and solution isn't explained in any of the documentation or game news, and the automation doesn't provide any notice.
Item #3 of the War documentation states:
"The maximum number of weapons per military base is 20.000."
Generally, the documentation treats carriers and fleets as bases. If the maximum number of weapons per carrier or fleet is 1,000, then it would be very helpful for the documentation to say that.
Also, it would be very helpful for the country newspaper or automation to provide a notice when a carrier or fleet has so many weapons that it can't move.