第二句话:The first steps were too foster economic cooperation:
主语:The first steps
系动词 were
表语: to foster economic cooperation
冒号之后是去对前面进行解释,它不是一个句子。
the idea +现在分词短语是冒号后的主体结构。being 后that countries ⋯是being 的表语。
表语中
that trade with one another 是定语从句,修饰countries.
become 是表语部分的谓语(countries become...)
independent 是become的表语, economically 副词作状语。
and 后面的也是become 的表语。