Military Access is automatically granted to everyone that shares a faction with you as well. The main use for Military Access is to get to the territory of an ally that you have no direct connection with. Let’s review it all below.
Getting & Giving Military Access
To view Military Access options, open another nation’s Diplomacy tab. You can do this by right clicking on one of their owned states. You’ll see two buttons that specify “Ask for military access” and “Offer military access”. These will show up among the Diplomacy options. If you hover over the options, you can see a prediction for what the country’s response to the proposal will be, along with their reasoning.
Best Uses for Military Access
Military Access’ best use is reaching an ally’s territory when you don’t have a direct connection to them. For example, in the image above, Czechoslovakia’s troops have no way of reaching Yugoslavia for help. The best course of action would be asking Germany, Romania, or Hungary for Military Access. However, if for example we asked Germany for military access, we could only go into Yugoslavia’s territory and not Italy’s territory. This is because Germany is not at war with Italy. Thus, Military Access works best for defending allies rather than going on the offensive.