China’s vow to shut down its commercial ivory trade by the end of this year was welcomed by environmentalists as a turning point in the fight against poachers. Activists cheered the government’s pledge for swift action, and the state-run news media called it a “monumental win for elephants.” But in making the decision, announced on Friday, to bring the world’s largest ivory market to a halt, the Chinese government also saw benefits for itself. The ban reinforced President Xi Jinping’s campaign against corrupt officials, who have been known to use ivory products as bribes.