Wed Sep 23, 2020 11:33 pm
Hi CTCitadel and welcome to the forum.
While warscore is important to being able to take a new region, loyalty is also a factor. Post an infantry unit in the region you desire to annex. Are you able to annex other regions, just not Venetia? If so, you will see a menu of eligible regions. If not, try to raise your warscore.
Corps do synch with adjacent armies. Do make sure the corps is attached to the army by clicking on the army and seeing if the corps flashes red. The corps commander's leadership, activation status, combat stance all add to the probability of corps marching to the sound of guns. But being adjacent is not an impediment. If you watch the combat log you will see the moment of engagement. The corps usually then joins the next combat round after engaging.
Perhaps if you mainly play as France, you are winning battles before adjacent corps can reach the battle. You might slow down how quickly battles are engaged in the options menu Game/Delayed Commitment. This might increase adjacent corps joining.