It would be "income inequality" - class warfare.
The current 'issues' in society are controlled by the progressive left, who constantly dream up and agitate societal issues.
Prior to 1914, there was neither an income tax in America, nor a federally syndicated central bank known as the Federal Reserve. Shortly thereafter, we had the stock market crash of 1929. This led to the suspension of the Gold Standard for the U.S. $20 and the silver standard for the U.S. $1 because the syndicated central bank was allowed to, essentially, print far more dollars than the treasury could back in held gold/silver assets.
This was an issue entirely created by the progressives, who insisted upon an income-graded taxing structure and espoused the virtues of a central bank being able to more accurately control the monetary supply and prevent things like market instability. In short, yes, the very thing progressives implemented in the U.S. to prevent stock market crashes and economic recessions (which were present, but very small in terms of percentage in decades prior) ... was the very thing that made the booming over-valuation of the market in the 1920s before it corrected in 29 and led to what was known as the Great Depression in America.
Of course, the progressives had a solution for that, too.
We got that in the form of social security (guaranteed retirement from the government, because the progressives made the stock market so volatile that entire retirements were obliterated and people didn't trust the market), government control of manufacturing output, etc. The 'New Deal' broke the spine of the U.S. economic recovery throughout the 30s. The only thing that saved America was the fact that Europe was involved in a war. Their farm hands and manufacturing workers were being drafted up to fight a war against an expanding Germany.
Since British pounds are essentially useless in America and to Americans - many of these nations were sending us gold and silver in shipments that allowed the U.S. federal government to act as a large revenue source for our economy during these times. The U.S. would have collapsed like Russia under the Bolshevik Revolution if it weren't for the fact that we were supplying Europe with considerable amounts of food, consumer goods, and munitions - we'd probably have fractured as a nation and many portions of the U.S. be little more than loose collections of farming communities.
The reason they keep bringing up the 'class warfare' argument in today's times is because they have essentially created the environment of 'crony capitalism' where the government regulation and control over industry has led to what is, essentially, a sort of fascism that benefits the financial and political elite.
There is still a lot of economic mobility and freedom, but it is becoming increasingly difficult for the average person to pursue business interests because of the amount of control the federal government demands over business in general. From hiring wages to health and environmental regulations, compliance fees, registration fees, etc - it raises the necessary investment capital to start a business and also increases the exposure to legal issues.
Take the cake bakers who now are being forced to pay large fines over 'damages' because they refused to make a cake for an event they did not feel comfortable supporting (a gay marriage). They can turn down making a cake that depicts a naked woman for a bachelor party, if they wanted to, I am sure - but if it's a wedding scene they don't feel comfortable with - they must make it or face a fine.
So, the issue will be class warfare. They will point to the system they created, claim it is evidence the free market doesn't work, and then propose that they do things even more like Stalin. Those who don't get to go to labor camps or some other form of camp where they are experimented upon for the benefit of the collective.
