Tanaka and Darvish have a better SO/9 in the USA than in Japan.

SO/9 final three seasons in Japan and then in USA:

Masahiro Tanaka: trending down in Japan:
2011 9.6 Japan
2012 8.8 Japan
2013 7.8 Japan
2014 10.1 USA

Yu Darvish: at the same age as Tanaka, trending up in Japan:
2009 8.3 Japan
2010 9.9 Japan
2011 10.7 Japan
2012: 10.4 USA
2013: 11.9 USA
2014: 10.4 USA

Yu Darvish with Texas struck out 221 in 2012 and led the league with 277 in 2013.

Both Tanaka and Darvish have a better SO/9 in the USA than in Japan.  Tanaka especially in his first 71 USA innings has reversed his downward trend and substantially improved his SO/9 in the USA.

Why?

We can only guess but one obvious explanation is the Ichiro Suzuki hitting style in Japan that emphasizes contact and going for singles over home runs.

The other reason may be that batters in the USA league are dumb.

Batters are dumber than usual this season, hitting into the shift most of the time.  April 7, 2014

March 13, 2012
By mjl816 via Wikimedia Commons