By the mid 22nd century the sun in Earth's system had begin to flare so badly as to precipitate a crisis.
All comms and many electrical devices were initially crippled for extended periods, particularly in the less developed nations and this was followed by issues of disruption to food distribution and shortage for earth's bloated population on top of disasters at power plants and rioting.
By this point several nations, and some private corporations had developed faster than light space flight and were pushing at interstellar exploration. When the crisis heightened at the discovery that the solar activity was slowly irradiating the population and remaining food, the advanced nations began work on ark fleets and military vessels to find new worlds that could support life.
Independently those that could, fled Earth, leaving those behind to a degenerative slide into desperate resource wars and mutation.
The fleets left for Messier 67, an open cluster containing hundreds of densely packed stars. By the end of the 23rd century colony worlds had been established and technology, access to new resources, and space to grow were fuelling a boom for many of the new nations and corporate world states. Humanity abhors a vacuum, and as such populations regrew from the colonists to result in exponentially expanding territories.
By the 25th century the new nations who had once been isolationist in their outlook or happy to trade and assist neighbours had begun to chaff on each others borders and eye greedily their neighbours resources. With disturbing rapidity the situation in many flash points began to worsen and dirty border wars, insurgencies and insurrection sprang up like bush fires...