The Encyclopedia Britannica defines the Salic Law of Succession as “the rule by which, in certain sovereign dynasties, persons descended from a previous sovereign only through a woman were excluded from succession to the throne. Gradually formulated in France, the rule takes its name from the code of the Salian Franks, the Lex Salica (Salic Law).”
In France the line of succession faced no problem of the male successor until King Louis X’s death in 1316. Although Louis’ wife delivered a male heir after the king’s death, the child passed within a week. Louis’ brother, Philip V, convened the Estates-General, which adopted a resolution that women would not be part of the line of succession to the French throne. The corollary principle also came into effect. With it, the children of a daughter of a French king could not make a claim to the throne. Salic law was used as reason to rebuff a claim to the French throne by England’s King Henry IV in 1410. The premise of Salic Law officially denied the infanta Isabella of Spain, the granddaughter of Henry II of France, her claim to the throne. Napoleon accepted the fundamental right of the practice, and it was applied to succession as late as the latter part of the 19th Century.
Succession to the English throne was different. It occurred in this precise manner: (1) Sons of the sovereign in the order of their birth and (2) Daughters of the sovereign in order of their birth. At the time of George III’s death, in order of succession we have George, the Prince of Wales, followed by the dukes of York, Clarence, Kent, Cumberland, Sussex, and Cambridge. The legitimate children of the heir (presumably the first born son) followed the rules likewise. There was, however, the stipulation that the daughters of the higher heir took precedence over any child of the heir’s sibling(s).
George III’s daughters produced no heirs to the throne, and his sons were well into their prime before they considered the family obligation of an heir to the throne. After Princess Charlotte’s death, George IV made no effort to produce another child with his wife Princess Caroline. York’s (next in line) marriage to Princess Frederica of Prussia produced no issue. 
William, Duke of Clarence, married (1818) Princess Adelaide of Saxe-Meiningen, but had no surviving issue. He did produce ten children with his mistress Dorothea Jordan, but they could have no claim upon the throne.
Prince Edward, Duke of Kent, was next line of succession. Replacing his long-standing mistress, one of 27 years, he married Princess Victoria of Saxe-Coburg-Saalfeld. Queen Victoria was his daughter.
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Ernest Augustus, Duke of Cumberland, was next in line. “He was the fifth son and eighth child of George III, who eleven years before Ernest’s birth had inherited the thrones of two kingdoms, Great Britain and Ireland, and also that of the Electorate of Hanover, still part of the Holy Roman Empire. As a fifth son, initially Ernest seemed unlikely to become a monarch, but Semi-Salic Law, applied to the succession in Hanover, and none of his elder brothers had any legitimate sons. Therefore, when in 1837 his niece, Victoria, became Queen of England and Ireland, ending the personal union between the British Isles and Hanover that had existed since 1714, Ernest became King of Hanover, which had been raised to a kingdom after the end of the Holy Roman Empire.” (Ernest Augustus I of Hanover)
Prince Augustus Frederick, Duke of Sussex, married in contravention of the Royal Marriages Act of 1772, to Lady Augusta Murray with whom he had issue. As this action eliminated him from the line of succession, the marriage was annulled in 1794. In 1831, he married Lady Cecilia Buggin, the Duchess of Inverness, but they had no issue.
Prince Aldolphus, Duke of Cambridge married Princess Augusta of Hesse-Cassel. They produced children.
Ironically, 1819 saw the birth of four children in the royal line. Clarence became a father legitimately in March. Neither that daughter, nor her sister two years later, survived. Clarence’s brother, Prince Aldolphus, produced a son born that month also, but the boy was well down the line of succession. On 27 May, Cumberland also greeted a son, who in other circumstances would have been the future ruler of both Hanover and the United Kingdom, except for the fact that Kent’s daughter Victoria came into this world three days before Prince George of Cumberland on 24 May 1819. Before long, any claims of her rivals to Victoria’s rise to the queendom dissipated.
Ironically, the Salic Law of Succession was applied when Victoria, who was from the House of Hanover, became queen of England in 1837 but was barred from succession to the Hanover crown, which went to her uncle Cumberland, whose son she usurped.
