Starting a business was relatively easy, and until 1913 with the introduction of income tax, transactions, including work for hire, could be done with non-monetary exchanges. Apprentices could be supported with room and board while they learned their trade, farmers could exchange food for goods and services, businesses could thrive all without a dollar ever changing hands.
Income tax, providing support for the Progressive idea that government needed more power, changed all that. Besides requiring all exchanges to be in the form of taxable monetary income, it gave government enormous power over commerce and the people who conducted it.
The free exchange of value which is the foundation of Capitalism, was now constrained to take place in monetary form only. Taxes have always given governments power. Rome was built on the tax tributes of its colonies. Later empires followed suit, but the imposition and collection of taxes was often haphazard and unreliable. An Income tax fixed those problems.
Our government was originally intended to be supported through tariffs and provision of certain essential services such as a postal service that would only charge for service rendered. Limitations on its income would limit its size so as to reduce its threat to individual liberty. It would be a government that was accountable to its constituents and not to itself.
An income tax, measured in money, that required every individual to report under penalty of severe punishment by government authorities was ideal. Al Capone, the famous gangster of the period shortly after the introduction of income taxes was convicted of failure to pay income taxes, not of murder, or drug dealing, or bootlegging, or gambling or any other criminal activity—income tax evasion! The Progressive idea of taxing income had a profound effect on the nature of work, on commerce, on how citizens interacted, made government larger and more intrusive, and even created an entirely new category of criminal activity.