Which reason most closely illustrates why the national government was on able to maintain law and order under the articles of confederation

The correct answer is A. There was no national court system.

Indeed, the other options refer to law-making or the economy whereas option A refers to law enforcement. Without a court system how could a nation that was supposed to be democratic have a semblance of rule of law, let alone be able to put criminal offenders to trial? It was with the creation of a national court system that this issue was appropriately solved.