How has the government role in contract regulation changed since the founding of the united states?

This depends on who the parties are to the contract and what the subject matter of the contracts contains. For instance, export control laws (which are federal) greatly affect sales between citizens and foreigners (even legal residents of the USA who are foreign nationals). The Contracts Clause of the Constitution has been left pretty much alone, but the Commerce Clause is frequently used instead to regulate contracts. Tariffs and Taxes directly affect sales contracts throughout the USA at both the federal and state levels. At the state level, Sales Tax is the biggest culprit. At the federal level, import and export taxes, capital gains taxes, etc. affect contract negotiation. Now, the USA is faced with another interesting problem: The Uniform Electronic Transactions Act and mortgages. The UETA allows al states who adopt it (in full and with no changes) to electronically sign contracts. This means it you don't have to sign for your mortgage with a pen and paper. Instead, you can do it via email in many jurisdictions. This is a HUGE problem with the "mortgages", especially for "robo-signing". There is a lot of debate in the federal circuit courts as to whether a mortgage foreclosure requires the "original" document or not. With e-signing, there is no true "original", but instead a digital image of the email/acceptance.