You are a rogue state with limited resources, and you want to make more powerful rockets. What is your improvised expedient? The answer, be it in North Korea or (with the most documentation) in Saddam’s Iraq, is frequently to cluster existing engines.
And what kind of engines would they be? There are the ubiqutuous Scud derivatives, but there’s also something even more readily available-surface to air missile engines, especially those (ie, SA-2s) becoming ever-less effective against actual opposing planes. Iraqi rocket/missile designs made extensive use of repurposed Guideline engines.
It’s gotten to the point where I’ve been making (oversimplified, of course) hypotheticals using the launcher and ballistic missile online calculators. Just input the relevant characteristics, thrust and size dimensions for the engines/rockets in question, and see the result! Quite an interesting bit of diversion for me.