This is history from a few years ago now, but was wondering if anyone who remembers CO's alliance strategy could help me out.

In mid-2008, Continental announced that it would leave SkyTeam (which occurred in late 2009) and join the Star Alliance. As part of this move, CO applied to join the Star Alliance ATI and joint venture. I believe the ATI covered 9 carriers prior to CO's entry (UA, AC, LH, BD, SR, LO, OS, SK, TP), and the JV (Atlantic ++) would include CO, UA, AC, and LH. Of course, the merger meant that UA/CO became one entity altogether, rendering the cooperation on int'l routes moot (though still relevant for the combined entity to have ATI/JV with the int'l partners).

A big rationale for CO's move to Star was that it was shut out of the SkyTeam ATI and JV. There was a long-standing ATI/JV between NW/KL and ATI between other SkyTeam partners DL, AF, AZ, and OK. In 2008, these ATIs were "merged" allowing collaboration among all the partners, with a JV among DL/NW/AF/KL. This pre-dated the DL/NW merger but of course became stronger after the merger and has since expanded to include AZ.

Why was CO never part of the SkyTeam ATI? (Its position was similar to US's in Star today, as US is not part of the Star ATI and does not cooperate with Star partners on any routes).

I assume it is because it never would have been approved given CO/DL overlap in the NYC market. But I've looked through many press releases and DOT filings and it seems that, from the beginning, CO's strategy always had it independent of its SkyTeam partners.