But at the movement’s root is a dramatic shift in identity since Britain pull
ed out in 1997 that has left a majority of Leung’s generation rejecting ties
to mainland China and asserting what they see as their own distinct and entire
ly separate identity.
很长有点高拐的句子但是这里since做为连接词表达“自从”意思时，开头的子句不需要
使用完成式吗？

谁说since后面必须接完成式的？没这回事。