It would be interesting to look at how Subsidies for particular industries have changed over the same periods. Is there any discussion about how domestic subsidies can impact on Trade?

If one of the reasons why tariffs have went drastically down in the 20th century is that governments have started to increase the personal income tax, then shouldn't the positive effect of lower tariffs on world trade (and thus GDP growth) be examined in view of the raising personal income taxes leading to lower disposable income, then lower savings rate and ultimately lower GDP growth? I.e. what is the net effect of lowering tariffs but raising personal taxes on GDP growth?