It was only in 1920 that the majority of white Americans were allowed to vote

Thomas Sowell is a gifted non-fiction author with a wonderful breadth of knowledge to make striking juxtapositions of data.  As in the instance from Conquests and Cultures by Thomas Sowell.  

The dire poverty of the early nineteenth century Irish may be indicated by their average life expectancy of 19 years—compared to 36 years for contemporary American slaves—and the fact that slaves in the United States typically lived in houses a little larger than the unventilated huts of the Irish and slept on mattresses, while the Irish slept in piles of straw.  Slaves also ate a wider variety of foods, including low grades of meat, while an Irishman, subsisting on potatoes and occasionally fish, might not see meat from one year to the next.  Bad as these "normal" conditions were among the Irish masses in the early nineteenth century, worse conditions followed in the 1840s, when potato blight destroyed the crop that provided their basic nutrition. 

Sowell is not arguing against the moral outrage warranted by chattel slavery, merely emphasizing that there are many forms of lost freedom and there is always a material context to be considered.  The moral case against chattel slavery is as robust as ever.  But 19 year life expectancies for Irish and 36 years for American slaves in the 1840s?  That is astonishing.  

Somehow turning this Irish peasant/Chattel slave anomaly over in my mind eventually led to a question in my mind.  American democracy has never, by design, been pure.  The Founders were extremely attuned towards the history of direct democracy becoming majoritarian mobs.

Beyond the Federal system and the three part divided government serving as checks and balances, there were all sorts of restrictions on who could vote from the very beginning.  Even though those restrictions were less onerous than virtually every other nation in the world at the time, it still shocks the modern conscience.  Restrictions such as being literate, or owning land, or paying taxes, etc.  

My question was, by what date could the majority of White Americans vote?  Given that women could not vote until the 19th Amendment which was only passed in 1920, it seems likely that 1920 was the earliest data by which a majority of whites were enfranchised.  

Women were allowed to vote in several states during the Revolutionary era but by 1807, no state allowed women to vote.  In the 1870s some thinly populated western states began to extend suffrage to all women but in terms of all whites, that was a tiny number.  

In 1776, Catholics, Quakers and Jews were not allowed to vote.  Up until 1965 poll tax tests were still used to deny the vote.  In 1966 The Supreme Court handed down a ruling outlawing the use of the poll-tax as a condition for voting.  

My guess is that, even with some states still having property and tax restrictions, 1920 was the first election in which voting rights were extended to the majority of white Americans.

For African-Americans it came slightly later.  While they had the right to vote by 1870, it still excluded women.  When did the majority of African-American have the right to vote?  Again, in 1920 with the 19th Amendment.

For blacks, the majority might not have been reached until 1966 with the Supreme Court's rejection of limits such as poll taxes became the law of the land.

For all of American history from 1607 up until 1920, the majority of Americans were unable to vote by law.  By 1966 most of the state restrictions (land ownership, literacy, poll tax, etc.) were also illegal.  

In a narrow window of time, 1920-1966 all Americans of all races were legally entitled to vote.  Before 1920, by law there was no racial group in which the majority of adults were allowed to vote.  

This is no argument against the excess burdens imposed on African-Americans between 1870 and 1966.  

All it is is a recognition that we rarely take the reality of the past into account.  It is nearly as shocking to me that the majority of whites were not allowed to vote until 1920 as it is that the Irish had a life expectancy nearly half that of American slaves in the 1840s.