I was looking at Islam in Europe's wiki page and it lists Armenia as having less than 1% Muslims and Spain as having 2-4%.
I would have thought they would have much more; Spain was once ruled by the Islamic Moors and is relatively close to Islamic North Africa.
Armenia's neighbors have extremely high Islamic populations (Azerbaijan has a population of 90-100% Muslims), so why does it have such a low population of Muslims?
This only covers Spain, but this answer by /u/drylaw discusses the experiences of the remaining Muslim population in Spain after the Reconquista.
Much like the fact that Jews and Muslims were expelled from Spain after 1492, Azeris gradually left the territority of Armenia, sometimes peacefully, sometimes violently. In the earliest Soviet Censuses, Azeris were about 10% of the Armenian SSR’s population. Some Azeris, along with other Turks, were “moved away from the front” in the late 190’s when Stalin was preparing for a war with Turkey (like the Meskhetian Turks of Georgia were starting in the 1944). After this period of force migration, there was more slow, voluntary migration, to the point where by in the 70’s and the 80’s Azeris and other Muslims made up closer to 5% of the Armenian SSR. In the late 80’s, as the eventual breakup of the Soviet Union became clearer, there were more riots, pogroms, and expulsions. The most famous of these occurred in Azerbaijan (the Sumgait Pogrom of 1988, the Baku Pogrom of 1990), but there were also some such events, at a smaller scale, on the Armenian side of the border (I think at Kapan and Masis in 87). In this environment where violence seemed likely, many “chose” to move and, in response to what was going on on the other side of the border, the threat (and sometimes reality) of violence increased. As Azerbaijan and Armenian got into a shooting war over Karabakh, many outright fled. In this period, for example, the main mosque in Yerevan was destroyed.
The Wikipedia article for Deportation of Azerbaijanis from Armenia has the following chart
| Census Year | Percent of Armenian SSR Azeri |
|---|---|
| 1926 | 9.6 |
| 1939 | 10.2 |
| 1959 | 6.1 |
| 1970 | 5.9 |
| 1979 | 5.2 |
| 1989 | 2.5 |
| 2001 | 0 |
As you can see, the decline is mostly due to a few clear incidents of violence: the state’s forced expulsion in the 40’s, the environment of threats in the 80’s, the outright war with Karabakh in the 90’s.
Pretty much whenever you see something like this on a map, it’s the result of a similar dynamic of flight and expulsion (and, in the worst cases, outright systemic policies of murder).