For some reason, the British royal marriages have fallen into endogamy for some reason.
The British royal cousin marriages are considered an example of endogamy, or the practice of marrying within a specific class and social group, often for financial gain or influence in affairs of state. The handful of first-cousin marriages was not out of the norm for their time.
After the 11th century, in only two cases there is no known familial relationship. Neither woman was queen consort. Both marriages were considered scandalous for their time.
The first wife of James II was the only daughter of a wealthy man, but with no pedigree. The marriage did produce two future sovereign queens.
Edward VIII married Wallis Simpson, and cited his desire to marry the twice divorced American woman as the reason for his abdication in 1936.