It's 17 years after the return of Voyager. The Alpha quadrant has been preparing for the return of the Borg, primarily by investing massive R&D in offensive and defensive weaponry. During the long peace, the Federation/Klingon alliance has been wearing thin, with the younger factions seeking a return to the old ways. Meanwhile, the Federation, taking advantage of a détente with the Romulans, have cautiously begun to work to with them on "holocloak" technology -- a combination of a "holodeck" and a cloaking device. Technically, this is a violation of the treaty of Algeron, which forbids the Federation the use of cloaking technology. While the treaty is technically between the Federation and the Romulans, the Federation's willingness to forgo cloaking is a linchpin of the Federation/Klingon alliance.