Internal revenue refers to taxes imposed directly on individuals or entities, mainly based on income. Historically, it has been a central topic in legal and economic discussions, as illustrated by 19th-century debates on financing infrastructure through tariffs and internal levies, as mentioned in The Continental Monthly. Legal experts such as Byron White and Hugo Black later examined its implementation, differentiating corporate profits from individual taxable activities in key court rulings.
At the same time, Alice Stopford Green pointed out medieval equivalents, such as "lyvelode," an early version of income tax. These diverse viewpoints highlight how internal revenue has transformed from a mechanism of fiscal policy into a complex legal framework, reconciling governmental requirements with personal financial circumstances.