[4] http://www.justfacts.com/images/taxes/federal_state_local_re...
I keep forgetting state and local taxes. I'm from Texas, which doesn't have a state income tax; I'm living in Alabama, which has an income tax rate of something like 4%. Both localities rely heavily on sales taxes to a typical tune of about 9% (and sales taxes are regressive, I'll remind you) and property taxes.
Anyway, check this:
http://taxfoundation.org/article/short-history-government-ta...
Chart 1 duplicates your graph's "Current Revenues" and "Current Spending" lines, while Table 1 shows total gov't receipts as a percent of GDP by (roughly) decade since 1930. In 1950, 22%; 1980, 28%; 2000, 31%; 2012, 26%.
So yes, taxes have gone up. But not spectacularly, certainly not as much as deficit spending, and probably not to the excessive detriment of the "moneyed elite".
You know, if the rich were actually suffering under confiscatory taxes, their percentage of total national income and wealth would be in the decline, but actually it has been steadily going up. Were you really not aware of that?
Donald Trump's campaign is populist, not whatever-the-political-opposite-of-elite-is. He is tied for #121 on the Forbes 400, after all.[1]
I don't actually know enough about Brexit to tell what the hell is going on there (like a lot of people, apparently). I do know that some people[2a] are very unhappy that David Cameron called a referendum instead of going through parliament.[2b] See also populism. My feeling, however, is that the anti-immigration thingy has more to do with the UK's own inequality situation.
Individual income taxes have been hovering between 6% and 10% of GDP since WWII; overall taxes have been between 15% and 20% of GDP since WWII.[3]
Now, as far as power being the problem, to the extent of my knowledge there are no facts in politics. All I've got is that, historically, concentrating power into the hands of a small minority seems to be a poor idea; and that most of the modern "rich countries" are de facto pseudo-democracies, apparently in an effort to avoid having ultimate authority concentrated in a small minority. YMMV. Some shrinkage may occur. Not for internal use. Do not taunt Happy Fun Ball.
[0] Unless someone's done gone and created a secret world government without copying me on the memo (Again, dammit!), rich countries' governmental structures should probably be treated in isolation. Particularly the US, which has remarkably little in common with "most rich countries".
[1] http://www.forbes.com/forbes-400/list/2/#version:static
[2a] https://next.ft.com/content/7877a0a6-3e11-11e6-9f2c-36b487eb...
[2b] http://www.economist.com/blogs/graphicdetail/2016/02/graphic...
[3] http://www.taxpolicycenter.org/statistics/source-revenue-sha...