What episode does the war start in One Piece?

At the beginning of the episode, Moby Dick and three other ships infiltrate the bay. Whitebeard announces that he has come to save his son Fire Fist Ace, and he had better be fine. Ivankov asked Luffy if Monkey D. Dragon would come to save Ace, as he wouldn't let his own son get executed. To Ivankov's shock, Luffy revealed that Ace is Gol D. Roger's son and not Monkey D. Dragon’s.

As Ace is being taken to his execution, he remembers the events that made him join the Whitebeard Pirates and become their Second Division Commander.

There is a flashback, where Whitebeard talks about his devil fruit. Before joining the Whitebeard Pirates, Ace was the captain of the Spade Pirates. Ace asks Jinbei to help him meet Whitebeard as he had turned down an offer to become a Shichibukai. Whiteboard had offered Ace the chance to join his crew and allowed him to become his Division Commander. Without Whitebeard's knowledge, Ace went to confront Blackbeard as he had turned against the crew and killed Thatch. When Whitebeard came after Ace, he asked Whitebeard why he came behind him to which Whitebeard replied that he shouldn't have gone alone to confront Blackbeard.

The flashback ends and Ace asks Whitebeard why he came to rescue him even when he disobeyed him, and Whitebeard replies that he'll always come to protect his son. The great Marineford War begins.

• The highlight of this episode is the reveal that Ace's real father is Gold D. Roger.

Q. Which crew was Ace in before he joined the Whitebeard Pirates?

A. Ace was the captain of the Spades Pirates before joining the Whitebeard Pirates.

Q. Till which episode does the Marineford Arc war last?

A. The Marineford Arc lasts from episode 461 to episode 489.