Idea for Sci-Fi novel. Man made wormholes are possible, but we don't have any true FTL travel. This means that humanity's expansion is limited to it's "light cone", at the time we get wormhole tech. What we don't realize is that there could be aliens limited by their own light cones, that by co-opting one of our wormholes they can essentially combine the two light cones into one, doubling their rate of expansion. This provides a hard-scifi setting where there can be a vastly technologically superior enemy, but where humanity still has a chance, as the initial wormholes act as natural choke-points and destroying them would stop the invasion.