I don't think the industrial decline seen in Britain had much to do with its colonies. It seems more like the newcomers being more competitive and innovative and the old dog not being able to learn new tricks.

The modern global economy is doing more importing/exporting than ever so we rely more on each other. The wildest China has done recently was to cut off Japan from some rare minerals and that lasted a few days IIRC. Among the greater powers no one is saber rattling like we saw a hundred years ago in Europe.