The catalyst for the confrontation was Galiana's research into shared consciousness, called Transenlightenment. Various breakthroughs led to the creation of the Conjoiners. Because a majority of the outer planets' populations (Mars, Neptune, the gas giants Saturn and Jupiter, etc.) were connected to the vast intra-system data network through implants, the Conjoiners sought to share their revelation with the rest of humanity through what amounted to computer viruses that would hijack an individual's implants and cause them to connect to others'. Experiencing a kind of joy and sense of unity previously unknown to humanity, they didn't comprehend that not all would want to join their collective. This action prompted the more conservative inner planets to fear for their safety from the "spiders", and pool their resources to fight what they perceived as a hostile takeover of the human race.
The Demarchists, meanwhile, were not co-opted, despite living primarily around the gas giants of Saturn and Jupiter, as they managed to firewall their implants en masse.