Before and during the Second World War, Germany made dramatic advances in rocketry and missiles. At the end of the war, the Americans, British, and Soviets grabbed up as many German scientists, technicians, and samples as they could lay hands upon. In the competition of the Cold War the military rocket programs of all three advanced by leaps and bounds. All passed beyond German capabilities by the late 1940s.
By 1951, the Soviet Union had developed nuclear weapons. The strategic question became how to use these weapons in war. The German V-2 had a flying range of 200 miles. Soviet missiles based on the V-2 would have to be fired from western East Germany and Czechoslovakia to bring Western Europe under fire. In fixed firing position, they would be highly vulnerable to air attack; in a Red Army advance, they would need to follow the frontline forward. Thus, mobile launchers offered the best solution. The V-2 launchers had been very cumbersome, so something more svelte would be welcomed.
In 1951, the Soviet high command issued a requirement for a V-2, but half as big. By mid-1955, the new missiles were starting to become available. Western intelligence agencies that figured out that the missiles were manufactured at the SKB-385 factory in Chelyabinsk oblast designated the new weapon as the SS-1B, and—I’m guessing–called it the Scud A. In any event, it could carry a nuclear warhead, but not very far: maximum range was 100 miles.
With this weapon in hand, the Soviets then got to work on a more robust successor. By 1964, the SS-1C Scud B had begun to enter service. It had double the range (c. 180 miles), much greater accuracy, and could be armed with a wide range of warheads for varied purposes. Over the years, the Soviets manufactured 7,000 Scud-Bs.
The Soviets transferred Scuds to clients. As part of their build-up of Egyptian forces in the early 1970s, the Soviets transferred some Scud-Bs for use against Israeli forces. Beginning in 1974 and continuing to 1988, the Soviet Union transferred over 800 Scud-Bs to Iraq.
Recipient countries then transferred them elsewhere. In 1979 or 1980, the Egyptians transferred a Scud-B to North Korea. The North Koreans then figured out how to make them for themselves. They tweaked the original design to improvement it, then called their missile the Hwasong-5.
In 1985, North Korea transferred to Iran perhaps 100 Hwasong-5s. The Iranians then did the same reverse-engineering as had done the North Koreans. They called their missile the Shahab-1.
In 1989, the Soviets transferred a large number of Scud-Bs to their client-state in Afghanistan.
Reverse-engineering is an education in itself. It enhances the technical capabilities of the people doing the work. If you put smart people to work, they start having ideas of their own. As a result, both North Korea and Iran have developed more highly capable successor generations of the original Scud-B. These, too, have been transferred.
So far, the AK 47 has killed more people in Third World Wars than has the Scud. So far.
 Kyle Mizokami, “How Soviet SCUD Missile Launchers Took the World By Storm,” The National Interest, 21 December 2021 How Soviet SCUD Missile Launchers Took the World By Storm | The National Interest; Sergio Pecanha, “Concerned About North Korea? The List of Missile Powers Keeps Growing,” NYT,11 February 2018.