Neon, i see what you mean. I am experiencing a similar thing in a scenario i'm playing; The Great Crusades by Joel Andre.
I'm playing as the Fatimids and i managed to get the Seljuqs to cancel our alliance and declare war on me. While i in turn allied myself with the Al-Andalus. All this to put my Machiavellian schemes in motion.
My intention was i'd push the Seljuqs from the Levant and Anatolia, while the Al-Andalus, with cities both in North-Africa and the Iberian peninsula, would consolidate their hold on the Iberian peninsula and occupy and soften up the French for my coming armies.
Now when i exchange maps i can see the Andalusians have tons of heavy equipment in North Africa bound for the Iberian peninsula, but somehow the AI is too stupid to load them in a transport and get them to the frontlines. Instead they just keep wandering around while on the other side they're getting slaughtered.
It seems the AI recognizes the connection between the two continents, by way of going round through the Sinaï, Levant, Anatolia, Danube valley etc., but not across the Straits which obviously is a shorter route.
Guess this is one of the reasons my Machiavellian schemes don't always work
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ugh crud, why won't they fall prey to my Machiavellian schemes?