The paternity of the sector theory is generally attributed to Senator Pascal Poirier who invoked it in 1907 as a basis for claiming sovereignty over all of the islands north of Canada. This attribution is accurate only in so far as he was the first to actually systematize the use of meridians of longitude to claim territorial sovereignty in the Arctic. The use of such meridians had been advanced long before to mark the delimitation of territorial claims.

Papal Bull (1493) and early treaties (1494 and 1529)

On May 4,1493, Pope Alexander VI issued his Bull Inter Caetera whereby he purported to grant to Spain ‘all islands and mainlands … towards the west and south, by drawing and establishing a line from the Arctic pole … to the Antarctic pole …, the said line to be distant one hundred leagues towards the west and south from any of the islands commonly known as the Azores and Cape Verde’. The Bull safeguarded previous grants to Portugal with a proviso that no similar right already conferred to a Christian prince was to be withdrawn.

On June 7 the following year, Spain and Portugal concluded the Treaty of Tordesillas in which they used a meridian of longitude from Pole to Pole to establish a boundary which alloted Spain ‘all lands, both islands and mainlands’ on the west side of the line and those on the east side to Portugal. The dividing line was fixed at a distance of 370 leagues west of the Cape Verde Islands, or in other words 270 leagues farther west than established by the Pope in the Bull.