Conflict with Scotland arose as many saw Mary Queen of Scots as the only one able to inherit the English throne, following Elizabeth getting smallpox in October 1562.
Fears of growing French influence with the potential marriage to the Duke of Anjou in 1579 (potential for an heir).
Elizabeth had Mary Queen of Scots executed in 1587, James VI of Scotland left with the best hereditary claim to the throne (protestant and had two sons as potential heirs by 1600).
Scottish relations were vested in religion and succession.
Mary QoS was criticised for her marriage to the Earl of Darnley, fled to England 1567 due to rumours.
Issues as some English Catholics saw Mary as the rightful heir, caused plots to overthrow, worsened following Elizabeth's 1570 excommunication.
Elizabeth signed Mary QoS's death warrant in February 1587, being seen as a martyr.