*Delta is tied with United.
*KLM and Northwest already operate as close to one airline
*NW owns the contolling stake of Continental
*CO has the option to buy a contolling stake of America West
*CO is codesharing with Air France and Alitalia
*Alitalia and KLM are closely working together
*NW and CO are or will be codesharing with AirChina
*Air France has indicated it will choose by the end of the year. (I think it will be chosen for them. It will be KLM's decision.)
*As for a potential NW/KLM/CO/Alitalia alliance, the only thing they'd be missing is intra-Asia. I don't think it would be too difficult to find an airline willing to join