The tax reform of 1986 eliminated the marriage penalty at the lower income levels. The marriage penalty did still exist, but only at higher income levels.
The tax oddity that we now call the “marriage penalty” came about in 1971. Let’s look at some examples.
This blog post gives a couple of examples of how taxes worked for married couples in 1920.
The treatment of marriage in the tax code was different 100 years ago than it is now.