Basic to any understanding of Canada in the 20 years after the Second World War is the country's impressive population growth.

　　(倒装结构Basic to any understanding…is…)

　　要理解二战之后20年中的加拿大，就必须了解该国惊人的人口增长。

　　分句1：Basic to any understanding of Canada in the 20 years after the Second World War

　　分句2：is

　　分句3：the country's impressive population growth

　　分句1，2，3共同构成倒装句，正常的语序应该是3，2，1，即：该句的正常语序是The country's impressive population growth is basic to any understanding of Canada in the 20 years after the Second World War.

　　本句是一个简单句，只不过使用了倒装，谓语动词是is.