I returned to the local used bookstore on Friday, and that's how we end up talking about Fed and Geoffrey Hoyle's Rockets in Ursa Major.
Mankind had been sending manned rockets into space for some time, but never hearing back from any of them. So they kind of gave up on interstellar exploration and focused on the Solar System, mostly trying to build a defense fleet, though it's unclear why they'd assume they needed to do so. Surprise, one of their rockets, one sent to ursa Major, does return, but it's empty, save for a single message: 'If this ship returns to Earth, then mankind is in deadly peril - God help you.' That's cheerful.
Soon enough, the aliens do arrive, and Earth realizes it's not on the level of its opponents. Fortunately, not all the aliens that arrive are hostile. There's one group that once had settled on many different planets, and whose names all seem to be those we've given to stars (the captain of the ship is Betelgeuse) but in so doing, aggravated a group called the Yela, who have since chased this race across the galaxy. The Yela are considered unstoppable, since their preferred tactic is to light a planet's atmosphere on fire. Fortunately, an Earth scientist comes up with an insane possible way to repel the Yela, and the book ends hinting at future conflicts.
One thing we learn about the Yela is they're pursuing this other group because they objected to how said group would colonize worlds, as this was perceived as a form of subjugation. At one point, Dr. Warboys suggests Earth and the this group try to negotiate, and is told the fact that Earthlings have advanced over thousands of years to become the dominant life form would be seen as subjugation, and the Yela would object. Then we learn the Yela have essentially press-ganged other races into their war against Betelgeuse's people, which sure as hell sounds like subjugation to me. But we're told they pursue Betelgeuse's people for that reason by one of his people, not any of the Yela, so perhaps it's conjecture.
In a certain way, this reminded me of Harry Turtledove's series about aliens attacking during World War 2. In those books, one of Earth's advantages was humans would act without concern for the future. The aliens had nuclear weapons, but were careful about setting them off because they wanted to live on the planet later. Humans didn't care, they detonated them as fast as they could build them, and would concern themselves with the fallout later. The Hoyles use a somewhat similar principal here, as Warboys' plan to repel the Yela seems ridiculously dangerous to me, but he figures defend Earth now, worry about the rest later. Once again, our self-destructive natures have saved us all. It does seem like a typical response. I don't think we really worry about a problem until it's happening, and even then it has to be dire before we'll take action. Otherwise, we figure the Earth will be the same tomorrow as it was today.
It's discussed that even though Betelgeuse's people are well advanced compared to Earth, Earthlings can develop new technologies faster. The idea seems to be Earth has provided a safe, stable home to work out new ideas on, whereas Betelgeuse's people are constantly on the run in space. If they try to settle a world, the Yela arrive and burn the atmosphere. As such, all the energies are focused towards keeping their ships running, which has made them highly efficient in that regard, but hasn't offered an opportunity for invention. Which sounds right. Not perhaps when dealing with Earthlings versus other intelligent species, but humans typically advance faster if they have some sort of home base, don't they? They could still venture out from it, but somewhere that's safe, and they don't have to focus solely on things necessary to survive right this moment can help things move along.
I do wonder about the other spaceships sent out from Earth. The one sent to Ursa Major wound up in the middle of a battle, and the Yela sent it back so they could follow it to the source. But that doesn't explain what happened to the others. Are they still in transit? Wildly off-course? Did they reach their destinations, but aren't able to contact home? Maybe they ran into problems other than the Yela. The answer to that might have been planned for follow up stories.