The strength of currencies has become a source of tension between some of the world's biggest economies, especially the US and China.

Brazil's finance minister went as far as to warn that his country would not stand idly by as international currency wars threatened its competitiveness.

What was he talking about?

Watch this animated guide to find out about why countries are falling out with each other because of their currencies.

It is likely to be one of the big subjects discussed at the G20 summit in the South Korean capital Seoul this week.