The First Order is an organization formed by the Imperial forces after the deaths of Palpatine and Darth Vader, continuing the Empire's mission to bring the galaxy under the rule of the Dark Side while using a different name in order to restore the Galactic Empire to its former glory. They were led by Supreme Leader Snoke until he was killed by his apprentice, Kylo Ren, who assumed leadership.
The organization is featured in the Star Wars Sequel Trilogy as the main villains, starting with Star Wars: The Force Awakens. They fight against the New Republic militia known as the Resistance. The First Order continues the Imperial tradition of using Stormtroopers as their foot soldiers.
The First Order was a remnant of the Galactic Empire, created when the Empire fell with the deaths of Palpatine and Darth Vader. After a year of fighting, the fracturing Empire made its last stand above the planet Jakku, where it lost to the New Republic in a battle that caused high casualties on both sides. Severely defeated, the New Republic forced the Empire to disarm and sign a treaty called the Galactic Concordance, in which the Empire was incredibly limited in its ability to wage war.
In the aftermath, those Imperial forces that did not and refused to comply with the New Republic's demands retreated to the Unknown Regions of the Galaxy, where they would rebuild. Over time, and to help rebuild their power, they entered into deals with corrupt politicians, tradesmen and gangs of outlaws and criminals. As the fragment that would become the First Order was small, it began work into creating soldiers, weapons, armor and warships that were technologically superior to the Empire to give them an edge. This edge was furthered when Supreme Leader Snoke, a powerful practitioner in the Dark Side of the Force, took the reigns as the organization's Supreme Leader. Among the advancements that emerged were several new types of starship, such as the Resurgent-Class Star Destroyer, more powerful armor and weapons, and Starkiller Base. The stormtroopers of the First Order, being fewer in number, were also better trained and better equipped than their Imperial predecessors; they were far more proficient than previous varieties of stormtroopers. They were conditioned since birth into serving the First Order willingly, and were indoctrinated to think that the New Republic had created lawlessness throughout the Galaxy, with their leaders stating that only the First Order could restore justice to the Galaxy, often using pre-recorded speeches to turn its citizens against the New Republic's "tyranny".
As the ranks of First Order grew, it became more and more bold, and began pushing into New Republic territory. As the New Republic did not wish to instigate another war, it was only able to formally protest against the First Order's violations against the treaties signed at the end of the Galactic Civil War. The expansion of its ranks was alarming, particularly to The Resistance, which privately fought against the First Order, and reconnaissance on their part was shocking in revealing the First Order's strength and numbers.
The First Order's military was comprised of Stormtroopers, just as the Galactic Empire's was. However, First Order Stormtroopers were far more skilled and better equipped than Imperial Stormtroopers and were therefore a much greater threat, despite being fewer in number. Several classes of Stormtrooper existed; among these were snowtroopers, heavy assault troopers, flametroopers utilizing powerful flame-throwers, and riot-control troopers, which specialized in melee combat and wielded powerful batons capable of even combating lightsabers. The First Order also deployed such vehicles as walkers not dissimilar to the Empire's AT-AT's and AT-ST's (though little is known about them). The First Order's navy was predominantly comprised of Star Destroyers, including older, Imperial models and new, massive Capital ships such as Kylo Ren's flagship, the Finalizer. Despite the Finalizer's size (twice the size of an average Star Destroyer), The Resistance believed that even bigger ships existed in the organization's ranks. The Military itself was led by both the generals of the First Order and the Knights of Ren, Snoke's organization of loyal Dark Side Force users led by him and his apprentice, Kylo Ren. Both branches of command answered directly to Snoke, though they competed against one another, likely because both the authority and agendas of the knights and Kylo Ren trumped that of the generals. Tensions were made higher by the fact that the Knights of Ren were not part of the First Order's formal hierarchy and operated freely and of their own volition under Snoke's orders. In addition to these, an organization of Praetorian Guards served as the Supreme Leader's bodyguards, and protected him against all threats. Armed with various melee weapons as well as lightsaber-resistant and blaster-proof armor, they made up a formidable force that surpassed the normal Stormtroopers in ferocity, skill and power.
The First Order also had no planet serving as its true Capital, as their Supreme Leader's true base was mobile, but Starkiller Base served as an unofficial headquarters for the organization, particularly during its attack on the Hosnian system and the attempted attack on the planet D'Qar, the site of The Resistance's headquarters. When the superweapon was destroyed by the Resistance, Supreme Leader Snoke merely told General Hux to evacuate and bring Kylo Ren to him for further training after Kylo had killed his own father, Han Solo. Snoke also had his soldiers regroup so as to fight another day. Snoke's true base, the Mega-Class Star Dreadnaught Supremacy, was a truly terrifying vessel, far larger and more powerful than even the Super Star Destroyers of the Galactic Empire.
Sometime after the Battle of Jakku, the First Order was founded by Snoke from the remnants of the Galactic Empire, three decades after the Battle of Endor, the First Order would largely escape galactic attention, with many in the Galactic Senate believing that it posed no real threat to the galaxy at large, with Chancellor Lanever Villecham arguing there was no need for concern as long as it adhered to the dictates of the Galactic Concordance. Despite this, the First Order blatantly defied the accords by ushering in the mass mobilization of superior stormtrooper forces, along with violating Republic bans on the sale of weaponry to the First Order and its rules governing capital ships. Testing the resolve of the New Republic, small skirmishes would occasionally erupt between the First Order and the Republic, all while the Starkiller operation would seek a suitable planet for implementation.
Approximately thirty years later, the First Order destroy the New Republic's current capital on Hosnian Prime, seeking to end its unofficial support of the Resistance with a new superweapon known as the Starkiller Base, which could fire a planet-shattering beam through hyperspace, and destroy an entire star system. With the destruction of the Republic's capital and a portion of its fleet, the First Order stood poised to destroy both the New Republic and the Resistance.
Much to its chagrin, former deserter Finn - along with Han Solo and Chewbacca would arrive at the Starkiller Base in an attempt to disable its shields and allow the Resistance Fleet to destroy the battle station converted planet. With the First Order fifteen minutes away from destroying the Resistance's base on D'Qar, the trio would not only manage to shut off the planet's shields but also rescue Rey after a lightsaber duel with Kylo Ren. Escaping the planet with seconds to spare, the First Order's sun-harvesting superweapon would be destroyed by the Resistance's Starfighter Corps, forming a new star where the planet once was. Despite this major setback, the First Order's resolve towards galactic conquest only increased, with Snoke deciding to finish Kylo's training and re-group after the destruction of his superweapon.