If you take even a casual look at American history, you will see that major social changes commenced in about 1830–e.g., the Abolitionist movement, Nat Turner’s revolt, first-wave feminism, the 2nd Great Awakening. Why? One major factor was improved transportation. The Erie Canal opened up the Midwest and made New York the largest and richest city in America. Train travel was another factor. People moved around more, spread ideas and technologies, etc. The roads and trails for conventional travel were also improved. The Oregon Trail started taken wagon traffic in 1836.
Looking deeper, we can ask how the Erie Canal (completed in 1825) and the railroads came into being, or the necessary preconditions. One essential element was iron ore. The canal, the railroads, and the trains themselves were made possible by iron technology. Try digging the Erie Canal with wooden shovels or sharp rocks.
Another factor was the invention and spread of telegraphy, which used the railroad right-of-ways. Another metal, copper, was essential to telegraphy. And, of course, large scale copper mining depended on iron and steel (an alloy of iron and carbon) tools and machinery.
Starting in about 1820, coke from coal replaced charcoal in the iron smelting process. The Erie Canal and the railroads soon brought iron ore east to New York and Pennsylvania.
These technologies were actants in an assemblage (see Latour, DeLanda, and others). And the assemblage facilitated more and faster communication. This is the connection to social systems theory. Social and psychic systems structurally couple with all kinds of technology and material artifacts.
The so-called Long Eighteenth Century has been dated from as early as 1660 to as late as 1832. (Dejean, J. (2012). A Long Eighteenth Century? What Eighteenth Century? PMLA,127(2), 317-320). But I am more interested in the end than the beginning. What event(s) do historian use to mark the ending?