@sgn15:
yeah. a bunch of pirate crews just surrendering their dreams to become pirate king to become allies with the strongest man in the world just doesnt sound right, especially if some or all of them were pirates who were beaten by WB like Ace and just surrendered after.
just imagine luffy surrendering his PK dream to become a division commander of WB or allied crew.. not so fast
I cant follow your argumentation. How is it bad to be a division commander? It is WBs pirate crew so there is nothing foul to be permanent in it. Franky e.g. could have his own crew without problems but he chose to be a straw hat pirate instead. That doesnt mean he had give his own dreams and ambitions off.
For the NW captains: I think it is a safe bet to assume, that this alliance is only temporary. A messenger or someone who had a close binding to a certain NW crew just came and asked if they would like to fight the World government. And not just shoot some flag over a courthouse down but a full out war against the heart of the marines. Something that maybe not even gold roger had dreamed of. And if the certain crew see a real change to win such a war, they jumped on the wagon.
If a half year ago some yonkou came and said: "Hey, it sure sucked, that the four emperors are meant to be on the same level but everyone see the WB pirates on top. So let just build an alliance of the three (or two) other yonkous alongside other famous NW pirates to bring the strongest pirate in the world down! Sound like fun, eh?" I think, the same pirates who now fought alongside WB would battle him and his divisions instead.
Another example: Say, that except aokiji akainu had cornered the SH pirates before water 7 and killed robin, the whole crew survived but dont see any chance to avenge their killed crew mates. And now came some yonkou or very powerfull NW pirat and propose, to build an alliance of pirate crews who have suffered the same losses to ambush and kill akainu. Luffy may know that this are rivals, but their common enemy is just too strong otherwise. That doesnt mean, he would give up his dreams.
Hell, luffy himself has allied on sabaody and in impel down with other foes or rivals allready.
All I want to say is, that some pirate crews on the alliance are fighting because deep friendship(like oars) or gratitude for WB, but most of the crews entirely because of fun and fame. If the war turned even more in favor of the WG I expect a lot of crews to abandon the alliance and leave. Or just turn the sides and attack WB himself.