I am specifically interested in the way that Democratization in eroded the influence of hereditary nobility in Western and Central Europe. Of particular interest to me are the territories of the former Austria-Hungary and of the German Empire. An interesting side topic could be any differences in the process between the Socialist DDR and the Democratic/Capitalist BRD.
I am a firm believer that although global standards of living have improved by leaps and bounds over the last two centuries, the world continues to be a deeply, deeply unequal place. But you don't have to take my word for it.
Although there certainly has been some convergence in wealth as incomes rise (and self-made men have occasionally taken center stage) by and large the top tiers of society continue to be very nearly inaccessible to a person born into a "Median Income" household, even in the wealthiest of modern societies.
But I'm breaking the twenty year rule. So what I'll do is point you to this answer on "Aristocratic Relations" I posted six months ago. There certainly is more room for discussion, especially with regards to the old "Eastern German" upper class' status in the Soviet Block, however I'll freely admit I'm ill equipped to answer that aspect of the question.
You can trace the fits and starts of democratization and limitations on the monarchy and aristocracy back well before the 19th century, but indeed it ramped up like a shot in the 19th. American influence on the French revolution, the French revolution's influence on Europe, Napoleon's continental spread of ideas, and then the disillusionment with empire and reset in Vienna. Add to this the industrial revolution and worker revolts...
People everywhere were mindful of what other people had (in other countries) and demanded the same. It spread like wildfire. Look to the French Revolution of 1830 and its spread outside of France to see some of the ebb and flow that would start things on the road to where the ancestral nobility finds itself now.