The north-west became the country's bread-basket.是什么意思？

The north-west became the country's bread-basket.

西北地区成为该国的大粮仓。

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

became

v. 变为，成为（ become的过去式 ）；

例句
It became very clear that the incident was not just an aberration, it was not just a single incident.
事实已经很清楚，这件事不是偶发的，它并不是一起孤立的事件。