In the early 20th century, U.S. federal and state prohibitions pushed cannabis from regulated commerce into underground networks. The 1937 Marijuana Tax Act effectively criminalized much of the trade and consumption, while international controls later consolidated under the 1961 Single Convention on Narcotic Drugs created a global prohibition framework. These policies didn’t end supply; they reorganized it—raising margins for smugglers and encouraging cross-border sourcing.

By the mid-20th century, cultivation for the U.S. market concentrated outside its borders. Mexico emerged as a primary source by the 1960s, supplying not only cannabis but other drugs as U.S. demand grew. The pattern mirrored broader drug markets: clampdowns in one region moved production and transit to another, but the U.S.–Mexico corridor remained central for marijuana.

The 1970s and 1980s professionalized the illicit chain. U.S. agencies reported ballooning consumption, and traffickers diversified transport: overland across the Southwest, coastal drops by small boats, and Caribbean and Pacific maritime routes. Florida in particular became a major off-load zone for “mothership” shipments feeding truck and stash-house distribution deeper into the country. U.S. interdiction efforts ramped up—DEA prioritizations shifted with heroin and cocaine waves, while the Coast Guard and Border Patrol expanded maritime and land enforcement—but networks adapted with new routes, compartmentalized cells, and improved concealment.

Even as domestic cultivation expanded, especially with the rise of indoor grows to evade aerial enforcement, the U.S. still drew significant volumes from Mexico and, episodically, from Asia (e.g., Thai/Cambodian product in the late 1970s–1980s). The illicit chain’s typical nodes were well established by then: source country grows → regional consolidators → cross-border smugglers → U.S. wholesalers → local distributors/retail sellers. That architecture—distinct roles dispersed to reduce risk—proved resilient to seizures and arrests.

Internationally, prohibition hardened supply lines but also fragmented them. The Single Convention and subsequent treaties pressed producer states to eradicate and criminalize, which often displaced rural economies into clandestine cultivation. In turn, traffickers integrated cannabis with multi-commodity smuggling (weapons, migrants, and later synthetics), using corruption and violence to safeguard corridors. Academic and policy histories show how cartel evolution intertwined with state pressure, electoral politics, and shifts in global drug portfolios; cannabis was once a main revenue stream before ceding primacy to cocaine and, more recently, synthetics—yet the cannabis routes and skill sets endured.

Legalization in parts of the U.S. since the 2010s changed the illicit supply chain again rather than eliminating it. High taxes, licensing bottlenecks, and uneven retail access created arbitrage opportunities. Some operators diverted legally grown cannabis into untaxed channels (“gray-market” leakage), while unlicensed grows—often with environmental harms—fed local and out-of-state buyers through the same wholesale-to-street ladders honed in prohibition. Enforcement data and reporting from California, the nation’s largest legal market, illustrate the persistence and scale of the illicit side in a post-legalization landscape.

Today’s illicit cannabis supply chain is thus a palimpsest: early 20th-century prohibition created the incentives; mid-century cross-border sourcing and maritime innovation built the infrastructure; late-century domestic indoor cultivation diversified supply; and modern partial legalization introduced regulatory arbitrage and diversion. Through each era, policy pressure has shifted—rather than erased—production and transit, while demand has continually financed new routes, intermediaries, and tactics. The net result is a market that adapts to enforcement and regulation alike, preserving many of its legacy pathways even as the legal industry expands.