We've all played zombie-themed games at some point in our lives, but in those we fought at most hundreds, maybe thousands. This time, however, we find ourselves fighting against billions of zombies. With its Steampunk style, this game depicts the struggle for survival of a group of colonists in a post-apocalyptic world.

     The game features 4 maps, but at first, you can only play the first one. For the others, you need to successfully finish the game at certain difficulty levels. You can also set how many days the game will last yourself. There are five different options between 80-150 days. The shorter the duration, the more frequently the zombies attack. Another difficulty setting is the number of zombies; in short, if there are too many, it will give you a headache. I recommend you start at the easiest settings to learn the game, otherwise, you will painfully learn how a tiny mistake can cause a massive destruction towards the end.

     To expand the colony, you need to build Tesla towers. You can't construct buildings anywhere without a Tesla tower. The Town Hall is the main place you must defend in this game. If this building falls, everything is over, the game ends and you lose. As long as your town hall stands and you kill the last zombie with your last soldier, you win, just make sure it doesn't fall. As the days go by, since the number of attacking zombies increases, you need to be quick. On certain days, zombies launch a massive attack from only one side of the map. On the last day, they attack from four directions of the map. Then, you understand why the game is called They Are Billions.

     As for unit types, there are the three: Soldier, Ranger, Sniper, and stronger units like Lucifer, Thanatos and Titan. According to your play style, you should build your army from these soldiers and be prepared for anything at any moment. These soldiers are used to kill wandering zombies already present on the map. Defense is provided by soldiers, walls, and various towers.