by the time the earthquake ended,millions of people had beco

直接became不可以.
因为by the time 是过去完成时的标志,看见这个标志,就一定要用过去完成时.
过去完成时的标志有：
1、by + 时间点
By last year,we had learnt 2 000 English words.
2、by the time + 句子,就是上面这一句
语法书里过去完成时部分重新翻一遍,语法书一定要经常翻,不翻就忘了