这里的it怎么指代？

Affording strategic proximity to the Strait of Gibraltar, Morocco was also of interest to the French throughout the first half of the twentieth century because they assumed that without it their grip on Algeria would never be secure.

这是一道语法题，划线部分是正确的选项，但我看不明白这里的it究竟是指代 Strait of Gibraltar还是the French，在这句话里难道不会出现指代歧异吗？

请教。。。

pronoun usually traces its antecedent in the main clause

嗯，之前是没弄懂of interest to的意思，所以没看懂句子结构，现在明白了，呵呵。。。