XCOM 2 by Rick Barba

In this original novel based on the hit video game, the Resistance gains new allies in fighting a new powerful alien enemy force.
Back in 2015, Earth's council of nations, facing an extraterrestrial onslaught, cravenly and abruptly surrendered to the alien invasion force. XCOM, the elite military unit created to defend the planet, was betrayed and forced underground. As Earth's survivors poured into the eerily clean and perfect New Cities, XCOM began to secretly rebuild and retool for a long-term guerilla war.
Twenty years later, homegrown pockets of resistance have sprouted in the hinterlands. Gritty bands of Reapers-expert marksmen and fearsome hunters of alien flesh-operate in the high-country wilderness. Tribal enclaves of former ADVENT Troopers-powerful human-alien hybrids called Skirmishers-roam the alpine passes of the Continental Divide, wreaking havoc on their hated former overlords. Other factions operate more overtly, some with mysterious and unsettling capabilities.
In response, the alien Elders have unleashed a lethal and terrifying new infiltration team called The Chosen. Can XCOM unite the resistance factions under its direction to counter this new deadly threat? Or will the alien escalation finally sweep away the last dogged defenders of human civilization?