After the Star River Envoy left, Markham and others naturally reported to the Solar System Alliance headquarters as soon as possible. Although the headquarters was prepared, they didn't expect the other party to arrive so quickly. It's very likely the wormholes were pre-arranged by them.
The Solar System Council discussed and decided on their first action, which was to cooperate, as the other party did not immediately resort to force.
Whether the opponent's claims are true or not, whether they truly possess such powerful force or were merely an amazing civilization putting on a show, time would tell. To mankind who had just emerged from a great war, being cautious was paramount. Of course, there were dissenting voices, but those thoughtless protests were suppressed. At least at this stage, the intelligence of human high-level decision-makers was fully operational, completely different from when they faced the giant worm.