How did China come to dominate global shipping?

The Donald Trump administration has said it will increase port fees on China-built vessels from October 14. Chinese-built and owned ships will be charged $50 (Rs 4,200) per ton in US port fees. That figure will increase by $30 (Rs 2,500) per year over the next three years. But why is the US making this move? Why is the world worried?

Explainers