One key element of the situation in 1920 was the growing northern concern about the disproportionate representation of slave state whites due to the infamous "three-fifths clause" of the Constitution of 1789. That was part of another famous Compromise. I'll let the reliably stodgy Britannica Online explain, from the article Constitution of the United States (internal links omitted):
The Constitution was the product of political compromise after long and often rancorous debates over issues such as states’ rights, representation, and slavery. Delegates from small and large states disagreed over whether the number of representatives in the new federal legislature should be the same for each state — as was the case under the Articles of Confederation — or different depending on a state’s population. In addition, some delegates from Northern states sought to abolish slavery or, failing that, to make representation dependent on the size of a state’s free population. At the same time, some Southern delegates threatened to abandon the convention if their demands to keep slavery and the slave trade legal and to count slaves for representation purposes were not met. Eventually the framers resolved their disputes by adopting a proposal put forward by the Connecticut delegation. The Great Compromise, as it came to be known, created a bicameral legislature with a Senate, in which all states would be equally represented, and a House of Representatives, in which representation would be apportioned on the basis of a state’s free population plus three-fifths of its slave population. (The inclusion of the slave population was known separately as the three-fifths compromise.) [my emphasis in bold]This created a bonus number of Congressional Representatives for slave states. As Sanford Levinson comments, "That compromise gave slave-owning states a bonus in the House of Representation and the Electoral College by counting slaves among those 'represented,' even though this was obviously a complete fiction." (Three-Fifths Compromise Was an Understandable Deal on Slavery New York Times 07/01/2015)
As always, it's important to keep in mind the extent as well as the limits of what American democracy was at this time. When the Constitution was written, the Framers were setting up a government for a democracy of white men, whose ability to vote could be and was subject to property requirements if states and localities so decided. Neither black men nor women or Native Americans were considered to eligible to vote by right.
Judith Wellman in The Road to Seneca Falls (2004) notes that New Jersey's 1776 constitution had extended the vote to women and blacks, subject to age and property requirements. "In 1807, however, the legislature used the occasion of widespread fraud in one local election to exclude women from voting. At the same time, they virtually eliminated property qualifications for adult white males." A great example in which an important step of progress (eliminating property qualifications) came joined at the hip with a huge step backward for the rights of women. It's also a reminder that real mischief can be done in the name of combating "voter fraud."
But it was also the case in 1789 that the Constitution envisaged a wider access to male suffrage and democratic control of government than European governments. This Getting the Vote website from the UK National Archives explains suffrage rights in Britain:
In early-19th-century Britain very few people had the right to vote. A survey conducted in 1780 revealed that the electorate in England and Wales consisted of just 214,000 people - less than 3% of the total population of approximately 8 million. In Scotland the electorate was even smaller: in 1831 a mere 4,500 men, out of a population of more than 2.6 million people, were entitled to vote in parliamentary elections. Large industrial cities like Leeds, Birmingham and Manchester did not have a single MP between them, whereas 'rotten boroughs' such as Dunwich in Suffolk (which had a population of 32 in 1831) were still sending two MPs to Westminster. The British electoral system was unrepresentative and outdated.By 1820, the premium representations the slave states were getting from the three-fifths clause were looking more and more "unrepresentuive and outdated."
The Senate itself was set up to give each state equal representation, which gave power in the Senate to less populated states equal to that of the most populated ones. And still does, for that matter. In 2017, California with its population of 39 million has the same number of Senators as Wyoming has with its 586 thousand. An individual voter's vote in Wyoming counts for a lot more in the Senate than one in California.
Democratic trends in American history have ebbed and flowed. Often at the same time. But the trend toward more democracy and equality was there. And as time went on since the ratification of the Constitution, the slavery bonus in representation from the three-fifths clause was looking less and less democratic to the voters of the free states. Freehling describes the initial arrangement established by the Constitution as "aristocratic Union." He writes, "Both North and South had to give in a little if aristocratic Union was to begin. Hence the resulting compromise, with each white counting as one soul and each slave as three-fifths of a human when apportioning each state's share of House seats."
It would be misleading to think of the ruling elite of 1787 as an aristocracy like those of Europe in the sociological-economic sense. But if we take "aristocratic" as a description of style and attitude, it gives us a useful perspective. Freehling argues that initially, "The three-fifths clause only slightly boosted the Slavepower's power." But he also points out, "If no three-fifths clause had existed and House
apportionment had been based strictly on white numbers, [John] Adams would have likely squeaked by, 63-61" in the Presidential election of 1800. It's understandable that even a "slight" boost that could make the difference in a Presidential election would be cause for concerned by the disadvantaged parties.
But the time, they were a'changin':
The nineteenth-century change from elitist to egalitarian republican sensibilities·best explains why the first mainstream northern assault on the Slavepower came not after the American Revolution but 40 years later, during the transition from the Age of Jefferson to the Age of Jackson. The three-fifths clause, which seemed republican according to aristocratic assumptions of the Age of the American Revolution, became anti-republican according to egalitarian assumptions of the Age of the Common Man. In state legislatures, city councils, and national presidential elections, leaders and followers insisted that the people, not the propertied, must rule. "The people" meant adult white males, ruling on a one-citizen, one-vote base. The three-fifths clause, awarding the Slavepower extra representatives for enslaved noncitizens, was the most anti-republican relic of a repudiated political outlook.As we'll see in later posts, the rising hostility to slavery and the slave power in the free states was not exclusively, or even primarily, a matter of moral concern, though that concern was real for many whites, as well. But as we see in this look at the three-fifths clause, the existence of slavery was diminishing and inhibiting democracy among the white males who were its only full citizens at that time. And the contradiction between slavery and democracy became stronger and more evident as the years went on.