(covers information from several alternate timelines)
A group of Na'kuhl from the 29th century led by Vosk escaped near-defeat in the Temporal Cold War, using a one-way form of stealth time travel, to reach Earth in 1944, in an alternate timeline created by multiple temporal incursions by various factions in the Cold War. There, the Na'kuhl constructed a temporal conduit in New York City in an attempt to return to the future. However, they were forced to use local materials that they secured through an alliance with Nazi Germans.
The primitive technology used made the machine enormous, and the Na'kuhl had difficulty keeping the conduit stable for more than a few seconds. After several failed attempts to operate the temporal conduit, the Na'kuhl were eventually successful, and traveled to the 31st century, where they defeated Daniels' faction and ignited the Cold War into an all-out conflict, resulting in the very alternate timeline to which they had originally escaped.
In an effort to stop the Na'kuhl, Daniels sent Captain Archer and Enterprise NX-01 to 1944, where they were able to destroy the conduit before Vosk could enter it. This had the effect of resetting the timeline to its proper form, and bringing an end to the Temporal Cold War. (ENT: "Storm Front", "Storm Front, Part II")