Deck and deal: one 52-card deck, no jokers, shuffled. Each player gets 26 cards face down. Nobody sees the order of either pile.
Ranking: Ace is highest, then King, Queen, Jack, 10 down to 2. Suits do not matter.
A battle: both players turn up their top card at the same time. The higher card wins both. Won cards go face down to the bottom of the winner’s pile, shuffled.
War: if the two cards are equal, they stay on the table. Each player puts one card face down, then one card face up. The higher face-up card wins every card in the War.
War again: if the face-up cards are equal too, the War carries on with another card down and another card up each, until one face-up card is higher.
Not enough cards: a player who runs short plays what they have. With one card left, it goes face up with no face-down card. With none left, their last face-up card stays in as their card for the rest of that War.
Winning: the game ends when one player has all 52 cards.