I would suggest an arrow from steam engine to Industrialization (not from steam power?)
I wouldn't also make Laissez-faire requiring marxism. It's a bit weird, because the theories are opposite to each other.
the Nationalism tree, I'm not satisfied with it

My suggestion (=means nothing

) :
======================Centralization====Marxism
==========================¦============¦
Nationalism -> Constitution -> Parliamentarism -----¦
==========================¦============¦
====================Foederalization==Laissez-faire
With each Centralization or Foederalization, you can build a small wonder. If the Centralization wonder is build, it's impossible to build the Foederalization wonder (Is this possible?)
And then:
================Marxism
==================¦
Industrialization --> economic theories
==================¦
===============Laissez-faire