China raised the standard of living of its people despite not only actual sanctions but even an actual grain blockade that was effected on them by the US via the UN, designed to starve them in the 1950s. The life standards rose in that decade too, not only after the 80s, and the US has nothing to do with it.

This is without saying that being able to trade with outside does not mean that the life standards of the people in a country will rise: The majority of the value from that trade would go to the minority capitalists in a capitalist country and a small percentage of white collars who do their bidding to run the companies owned by those, while the rest majority in the country can be living in knee-deep sh*t. We are seeing this today in various, formerly-prosperous countries even, including the US where a tiny minority takes the boon while the majority has to juggle multiple jobs to afford rent and food.