Message in a Bottle:ISMU

The Intra-Solar Military Unit, or ISMU, is the standing military force of the unified government of Earth.

Purpose

By the time the SPS launched their Forerunner probe, there was no more need for war between nations, for the historical nations of the world had finally formed into a single union. The ISMU had been formed before that final unification, and so in a sense was a historical relic, but even with one world government there was still need for the capacity to exert force.

For example, Earth was no longer the only inhabited body in the solar system. While the SPS worked to colonize the universe, other humans chose to look closer to home, and colonized nearby planets, moons, and even large asteroids. Colonies like Mars and Europa were ostensibly under Earth's jurisdiction, but the kind of people who pack up and move to another planet are often the sort of people dissatisfied with a large government. Left to their own devices they would surely revolt, and so the ISMU existed in part to prevent that eventuality.

The ISMU was also tasked with enforcing the Ceres Proclamation against slavery and human trafficking. With so much space in the solar system, unscrupulous people were tempted to return to that most profitable business: people.