I fought a war as Portugal versus Spain, France and the Ottoman Empire in a MP campaign some time ago. Toughest war ever. I was attacked by their combined fleet, which I, after initial defeat, managed to beat. That way I could store my ~120k army on the ships while the French-Spanish tried to take over my provinces.
The DoW came in 1556, and I had conquered much of Morocco and the gold of pagan West Africa, including Timbuktu. The French had attacked me some decades earlier, trying to take that gold away, but had been thwarted. Now they had swayed Spain against me and dowed, but I had been able to get to and past LT26, and thus had Mighty forts in the four Portuguese provinces (we were playing WatK). Once naval superiority was secured, and most of the enemies' ships sunk (my naval tech was far superior as well; I was the second richest nation in the world prior to the DoW, and by far the fastest techer), I could reinforce my army from Rabat, my Moroccan stronghold, and keep it in shape.
The initial attack from the coalition was around 1200 galleys with 200k troops from France and Ottomans and 140 Spanish galleys and about 70k troops. I had a navy of 530 warships and a standing army of about 110k, but quickly built up another 50k, which was all my manpower would allow at that time. Ships I could build at quite a pace however, with four Shipyards. I also had a 44k in Africa, to defend against colonial attacks from the French there.
The Ottomans WPed me shortly after their navy had been defeated, leaving me with Spain and France to deal with. But my Mighty forts were too hard for them to assault. They had much superior manpower, but could not capture my provinces. And time was on my side, as Brandenburg and Austria were only waiting for their NAPs to end, and would attack France in the back once the time came.
It came down to large Franco-Spanish armies trying to siege my provinces, and my ships sailing back and forth to chase away these armies, again and again. I could not go on the offensive, due to attrition and my poor manpower. I could not afford to lose any men, because I could not reinforce them. After about 11 years of this desperate defence, and including a thwarted French comeback on the seas, Brandenburg and Austria finally attacked, and France had to draw back their forces to fight the two off.
It should be mentioned that France had dominated the game since start, and had large holdings in Italy, had Venice vassalized (Holland too at a point) and were the clearly strongest military nation.
When French troops pulled back, the pressure naturally decreased on Portugal. Now I had the chance to beat Spain, and decided to demand Andalusia. The Spanish were stiff-necked though, and refused. And to stop me from force-peacing for that province, they asked France to place a 50k army there to stop me from attacking. Together with Spanish defenders, this made an attack on that province very expensive in terms of men, and I didn't have many. War Exhaustion was huge as well, since I had built my full manpower many times already. But Spain had not reached LT26, and they had mostly Minimal forts, so I sailed around with my navy and assaulted all their coastal provinces, quickly robbing them of manpower. Then I attacked and took their capital, and stabhitted them to -3 at which point I force-peaced them for 5 provinces. They still refused to only give me Andalusia (which I would have preferred to the 5).
This is how it looked after 10 years of war:
These 5 gave me a land border with France, and with all the battle warscore from the earlier parts of the war, I now launched an invasion from the south on France, occupying Gascogne, which had a Shipyard and a Large fort, and stahitted for it. The French, knowing they wouldn't fare well with many stabhits, accepted it. And then there was peace...
I later attacked Spain again, now with France NAPped, and took Andalusia. This led to the Spanish player resigning and come the 18th Century I had annexed them completely.
For the interested, stats can be found
here.
