The United States and Britain launched new strikes on Yemen’s Houthis Monday, saying their second round of joint military action against the Iran-backed rebels was in response to continued attacks on Red Sea shipping. American and British forces carried out a first wave of strikes against the rebel group earlier this month, and the United States launched further air raids against missiles that Washington said posed imminent threats to both civilian and military vessels. But the Houthis have vowed to continue their attacks — just one part of a growing crisis in the Middle East linked to the Is…