The 100 – Season 1, Episode 13 (“We Are Grounders: Part 2”)

In the season finale of The 100 Season 1, tensions reach their peak as the battle between the delinquents and the Grounders erupts. Clarke and Bellamy struggle to lead their people, knowing they are vastly outnumbered. Finn desperately tries to broker peace but fails, leaving them with no choice but to fight.

Meanwhile, on the Ark, Jaha makes a self-sacrificing decision, staying behind to ensure the remaining survivors can reach Earth. Kane and Abby lead the desperate effort to launch the last remaining dropships, sending the Ark’s inhabitants to the ground.

Back at the camp, the 100 execute their last resort: setting off a massive firebomb to wipe out the attacking Grounders. The explosion devastates the battlefield, but in the aftermath, Clarke, Monty, and several others are captured by the mysterious Mountain Men.

The episode ends with Clarke waking up in a sterile, high-tech facility, realizing they are now prisoners in Mount Weather.
The shocking cliffhanger sets up the next season, introducing a new and unknown enemy.