Obama’s QE2 (quantitative easing). As the US was mired in the 2009 global financial crisis, near the end of 2010, QE2 created $600 billion dollars to save the banking sector from failing. This created a high risk of commodity price inflation overseas, which would hit net exporter countries like China particularly hard since they import a lot of raw materials for their manufacturing sector.

China stopped buying USD and went into purchasing eurozone debt instead, because propping up the USD would only make their producer price more expensive. As the QE2 came to an end and the inflation was not as bad as everyone thought, China ditched the euro and resumed the USD purchase again.