Humanity had its back to the wall. After making the journey to space, we were approached by an extraterrestrial civilization. After extending a hand in peace, the alien menace opened fire on us. Entire cities crumbled, world leaders were humbled, and humanity nearly collapsed under the pressure. It was around this time that the civilizations of the Earth knew what had to be done. All nations called a truce, protected under the Darwin Movement. This act called to action all willing metahuman personnel to active duty as one team. Project Sentinel.
Based in every country, all over the world, these teams rose up to fight the alien menace with combat prowess yet unknown to any other race. Their technology eclipsed that of the world's governments. Their numbers outpaced the most densely populated cities in the world. They were the ultimate fighting force, and not even the combined might of an entire race could stop them. They couldn't stop the will to fight that the human race could muster up. Project Sentinel had won.
As the years went by, the Sentinels began to gradually shift to a world-wide police force. They kept peace among all countries, protected the innocent, and even decreased poverty with their offers of work. But with a group so skilled as the Sentinels, they were not without inherent flaws. The flaws of mankind. Corruption slowly began to seep in through the cracks. The Sentinels would side with one government over another, create wars rather than end them, conquer entire nations. And thus, the project was ended at a meeting called by the United Nations. All Sentinel activity ceased, and every facility was shut down.
However, while most Sentinels went down their own path, some still stand in the name of peace under their old banner. Accepting new recruits and holding true to the morals that they held so dear in the war. This is what they signed up for. This is what makes them Sentinels. They are the harbingers of a brighter tomorrow.