Anarchy: an absence of law or any enforcement of law.
Anarchy can occur where there is law but no-one to enforce it, such as a temporary or long-term absence of government and law enforcement.
In a 1925 case from a very quaintly named court of appeal, the "Supreme Court of Errors of Connecticut", State v Schleifer (102 Conn. 708), Mr. Schleifer made the following speech to his fellow strikers:
"You will never win the strike with soft methods. You young men ought to go out on the bridge. Don't use eggs, use coal or indelible ink. Break foreman's windows at their homes. Watch the scabs when they come from work, lay for them, especially on pay day. Take them in a dark alley and hit them with a lead pipe. That is the softest thing you can use. Reimburse yourselves for what we have sacrificed for five months. Don't forget to bump off a few now and then, so Mr. Pearson will know that you are not getting cold feet. You car men know how to take a brake shoe off. Take the brake shoe and put it under something that will put the cars off the irons. A little sand or emery in the journal boxes will help greatly. Don't be satisfied with trimming the engines. Put some of the cars on the bum. Also, if convenient, put something in between the frames and rods of engines on sidings. Get busy young fellows, and trim these scabs. Things are running too smooth on the New Haven Road, but let me hear from you while I am here. Go ahead and rip things and don't let the injunction stop you from trimming these scabs. Don't forget to tie them up with derailments. You boys ought to cut them all up."
In delivering the reasons of the Court, and in dismissing the conviction of Schleifer because of a technicality, Justice Wheeler adopted these words:
"Anarchy ... at its best, stands for a society made orderly by good manners rather than by law, in which each person produces according to his powers, and receives according to his needs.
"At its worst, it stands for a terroristic resistance of all present government and social order.”
In Olmstead v USA 277 US 418 (1928), it was said:
"Decency, security, and liberty alike demand that government officials shall be subjected to the same rules of conduct that are commands to the citizen. In a government of laws, existence of the government will be imperiled if it fails to observe the law scrupulously. Our government is the potent, the omnipresent teacher. For good or for ill, it teaches the whole people by its example.
"Crime is contagious. If the government becomes a lawbreaker, it breeds contempt for law; it invites every man to become a law unto himself; it invites anarchy. To declare that in the administration of the criminal law the end justifies the means - to declare that the government may commit crimes in order to secure the conviction of a private criminal - would bring terrible retribution. Against that pernicious doctrine this court should resolutely set its face."
See also the comments about anarchy in Origin of Law.