An exploit if you will, can be used when a country like the UK or France or any rich country trying to annex a country in an area you have declared an interest in, because you can join any diplomatic pacts taking place in that area, you can offer "help" to the European country you know is going to win, and ask for bankrolling, even if the country is the UK trying to annex some random country in Africa, they will most likely accept, even the German empire trying to attack isolationist Japan, I've done this many times and I have so many countries bankrolling me, this obviously needs to be changed, Britain doesn't need my help attacking some country in Africa for 20k - 40k pounds month.

Edit: I also want to add transfer states, I think the diplomatic pacts thing needs a change, you can literally get British states, under their direct control, for assisting them against African chiefdoms, even though, they absolutely don't need the help