Re: 2150 + 7 Years on TV = When TOS said they'd be an Earth Romulan Wa
They didn't even have to do a war arc. They could have done a series- long intermitttent version of the S4 "Romulan arc". Andorians, Tellarites and others would be catching "Vulcan" spies and saboteurs (which would have more logically fed suspicion and distrust of the Vulcans). Romulan agents, including the Suliban (an obscure species from the Romulan empire), seed distrust among the various species to ensure there can be no alliances. The humans are not distrusted because they're new to deep space travel -- in fact, being such late comers, Earth has been ignored by the Romulans as weak and irrelevant.
That gives Archer time to make first contacts and build relationships and trust with other species. The Romulans realize their mistake sometime around the end of season 6 when the coalition is formed. Then the attacks, spying and sabotage begin occurring against Earth interests (colonies, boomers, etc. and of course, Enterprise and Columbia).
The series finale ends with the appearance on Enterprise's long-range scanners of a massive invasion force from the direction of Romulus and Remus... and all Archer and Co. can do is run.