Ah, reinforcements Welcome to the Org, Lacker

Acumen does it, but the trade rules ultimately. We had some bigger discussions about that some month or two ago, do a quick search and you'll find many things. Actually, I didn't believe how high the income can be if based on trade – I played way too much with HRE only – but then I tried the Spanish and had some 30.000 to 40.000 income per year, all thanks to trading and keeping a low profile But when the total war phase begins and as you conquer more and more of the map, less trade income you will get. Save that money for rainy days