In the field of law, the word force has two main meanings: unlawful violence and lawful compulsion. "Forced entry" is an expression falling under the category of unlawful violence; "in force" or "forced sale" would be examples of expressions in the category of lawful compulsion. When something is said to have been done "by force", it usually implies that it was done by actual or threatened violence ("might"), not necessarily by legal authority ("right"). "Force of arms" is a special case that can be an example of unlawful violence or lawful compulsion dependent on who is exercising the violence (or threat thereof) and their legal right and/or responsibility to do so. When one citizen threatens another with a weapon, that would typically be an example of the unlawful expression of force of arms. The same threat expressed by a police officer making an arrest would be considered lawful compulsion.
