An allegiance is a duty of fidelity said to be owed, or freely committed, by the people, subjects or citizens to their state or sovereign.
[1] The word allegiance comes from Middle English ligeaunce (see Medieval Latin ligeantia, "a liegance").
[2] The English doctrine, which was at one time adopted in the United States, asserted that allegiance was indelible: "Nemo potest exuere patriam".
As the law stood prior to 1870, every person who by birth or naturalisation satisfied the conditions set forth, even if removed in infancy to another country where their family resided, owed an allegiance to the British crown which they could never resign or lose, except by act of parliament or by the recognition of the independence or the cession of the portion of British territory in which they resided.
[2] This refusal to accept any renunciation of allegiance to the Crown led to conflict with the United States over impressment, which led to further conflicts during the War of 1812, when thirteen Irish American prisoners of war were executed as traitors after the Battle of Queenston Heights; Winfield Scott urged American reprisal, but none was carried out.
Loyalty requires affection also to the office of the sovereign, attachment to royalty, attachment to the law and to the constitution of the realm, and he who would, by force or by fraud, endeavour to prostrate that law and constitution, though he may retain his affection for its head, can boast but an imperfect and spurious species of loyalty (R v O'Connell (1844) 7 ILR 261).
There were four kinds of allegiances (Rittson v Stordy (1855) 3 Sm & G 230; De Geer v Stone (1882) 22 Ch D 243; Isaacson v Durant (1886) 54 LT 684; Gibson, Gavin v Gibson [1913] 3 KB 379; Joyce v DPP [1946] AC 347; Collingwood v Pace (1661) O Bridg 410; Lane v Bennett (1836) 1 M & W 70; Lyons Corp v East India Co (1836) 1 Moo PCC 175; Birtwhistle v Vardill (1840) 7 Cl & Fin 895; R v Lopez, R v Sattler (1858) Dears & B 525; Ex p Brown (1864) 5 B & S 280): Natural allegiance was acquired by birth within the sovereign's dominions (except for the issue of diplomats or of invading forces or of an alien in an enemy occupied territory).
Denization, or ligeantia acquisita, appears to be threefold (Thomas v Sorrel (1673) 3 Keb 143): Local allegiance was due by an alien while in the protection of the crown.
All friendly resident aliens incurred all the obligations of subjects (The Angelique (1801) 3 Ch Rob App 7).
Instead of declaring fidelity to a monarch, the pledge is made to the flag, the republic, and to the core values of the country, specifically liberty and justice.