/u/Commustar has a fantastic earlier answer about Nubia, Jerusalem, and the Crusades that might interest you:

• Did Nubian Christians participate in the Crusades?

u/sunagainstgold has already linked to u/Commustar’s older answer, but hopefully I can add a little bit to it!

The crusaders and the Nubians were vaguely aware of each and Nubia was indirectly involved, but there was never a specific alliance. The crusaders and Ethiopians were also vaguely aware of each other, but Ethiopia was even further away, and it’s very likely that European crusaders had no idea they were separate countries.

Both the Nubians and Ethiopians were technically under the authority of the Coptic Church in Egypt. The Coptic Pope in Alexandria was responsible for appointing their bishops. At the time of the crusades, Egypt was ruled by the Fatimid Caliphate, which also considered Nubia and Ethiopia to be under their protection too - the Fatimids were responsible for protecting the Coptic Church so therefore they felt they were responsible for all Coptic Christians, wherever they were.

There were actually two kingdoms in Nubia at the time, the northern kingdom in Makuria, with its capital at Dongola, and another kingdom further south in Alwa (or Alodia). Further south past Alwa was the Kingdom of Axum in Ethiopia. Nubians and Ethiopians probably lived in Cairo and elsewhere in Egypt. In the 1080s, the Fatimid vizier in Cairo, Badr al-Jamali, was in close contact with Makuria and wanted to send Muslim merchants there and also build mosques there. But the Makurians were opposed to this, and overthrew their king, Solomon, who then lived the rest of his life in Cairo. Solomon was buried in the Armenian church of St. George.

The original crusaders at the end of the 11th century and into the 12th century probably didn’t know much, if anything, about Nubia or Ethiopia. The Fatimids controlled Jerusalem when the crusaders arrived, and the chronicler Fulcher of Chartres reported that the Fatimid army included “black Ethiopians”, but of course it’s equally likely that they were Nubians. The same “Ethiopians” were part of the Fatimid garrison that was allowed to leave Jerusalem after the crusader conquest in July 1099.

Otherwise there is virtually no mention of Nubians or Ethiopians in crusader sources in the 12th century. The only reference to Nubians is from a European pilgrim in the 1170s, Theoderich of Wurzburg. Nubians were among the numerous Christian groups he encountered in Jerusalem, although he doesn’t say anything else about them, just that they were there. It’s possible he was referring to Egyptian Copts, but unfortunately we have no idea.

In the 1160s, the crusaders had invaded Egypt, where they probably met Coptic Christians for the first time. Very briefly, their invasion of Egypt drew the attention of the sultan of Damascus in Syria, Nur ad-Din, who sent his general Saladin to intervene. Saladin defeated the crusader invasions, but he never left - in 1171, when the Fatimid caliph died, Saladin took the opportunity to overthrow the Fatimid government entirely. The Fatimids were Shi’ites so Saladin now brought Egypt back under the authority of the Sunni caliph in Baghdad.

The Fatimid dynasty tried to fight back. The Fatimid army in Cairo included Armenians and Nubians and when they were defeated in 1171 they probably fled to Nubia. In 1172, this Fatimid/Nubian army attacked the southern frontier of Egypt. Saladin sent his brother Turanshah to investigate and Turanshah captured the Nubian fortress of Ibrim. According to Ibn al-Athir, who was writing a few decades later in the 13th century, Saladin was interested in Nubia because he was still unsure about his conquest of Egypt. Nur ad-Din could have shown up to dislodge Saladin, so Saladin’s plan B was the conquer Nubia and live there instead. That seems pretty unlikely but that’s the story Ibn al-Athir heard, at least. Other 12th- and 13th century travellers to Nubia reported that it was wealthy and impressive so Turanshah was probably exaggerating its poverty, if this story is true. In any case

"there was little to be achieved in Nubia beyond punitive expeditions” (Lyons and Jackson, pg. 61)

The story of Turanshah’s expedition was completely ignored by Christian chronicles, such as William of Tyre, the court historian of the Kingdom of Jerusalem in the 1170s. but it does show up in some versions of the 13th-century French translation of William’s chronicle, the “Estoires d’Outremer”. The Estoires includes a long passage about Saladin’s war against Nubia that must have been known from a Muslim source. Wherever it came from, this was one of the first times that any crusader source mentions the Nubians in detail.

Another literary source is the French crusade cycle of epic poetry. One poem mentions that the crusader “Harpin” married the “queen of Nubia”, and retired to a Templar monastery after she died. Harpin was a real crusader, Odo Arpin of Bourges, but in the poetic cycle he’s clearly become a legendary figure.

In real life, the crusaders probably had no idea where Nubia or Ethiopia were exactly. In the 1180s the crusader Reynald of Chatillon tried to launch a naval expedition down the Red Sea, intending to attack Mecca. They apparently reached as far as Aydhab on the African coast of the sea, where they were captured by the Egyptians (some of the crusaders were taken prisoner and executed in Mecca). They apparently weren’t aware that Aydhab is close to Makuria and Alwa and they could have made direct contact with the Nubians if they had kept going.

Saladin eventually reconquered Jerusalem in 1187. The Third Crusade in 1190-1192 managed to recover the cities along the Mediterranean coast, but not Jerusalem itself. In Europe, it was recognized that if future crusades were going to be successful, they would have to eliminate Egypt first. The Fourth Crusade in 1202 was meant to attack Egypt, but for various reasons it ended up being diverted to the Byzantine Empire and captured Constantinople itself.

In Constantinople the crusaders happened to have their first direct contact with a Nubian king. One of the crusaders recorded the meeting:

"And while the barons were there at the palace, a king came there whose skin was all black, and he had a cross in the middle of his forehead that had been made with a hot iron. This king was living in a very rich abbey in the city, in which the former emperor Alexius [Alexios III] had commanded that he should be lodged and of which he was to be lord and owner as long as he wanted to stay there. When the emperor [the new emperor, Alexios IV] saw him coming, he rose to meet him and did great honor to him. And the emperor asked the barons: ‘Do you know,’ said he, ‘who this man is?’ ‘Not at all, sire,’ said the barons. ‘I’faith,’ said the emperor, ‘this is the king of Nubia, who is come on pilgrimage to this city.’ Then they had an interpreter talk to him and ask him where his land was, and he answered the interpreter in his own language that his land was a hundred days’ journey still beyond Jerusalem, and he had come from there to Jerusalem on pilgrimage. And he said that when he set out from his land he had fully sixty of his countrymen with him, and when he came to Jerusalem there were only ten of them alive, and when he came from Jerusalem to Constantinople there were only two of them alive. And he said that he wanted to go on pilgrimage to Rome and from Rome to St. James, and then come back to Jerusalem, if he should live so long, and then die there. And he said that all the people of his land were Christians and that when a child was born and baptized they made a cross in the middle of his forehead with a hot iron, like the one he had. And the barons gazed at this king with great wonder.” (Robert of Clari, pg. 80-81)

It’s not entirely certain who this king was but the timeline would fit Moses Georgios, who was king of Makuria and fought against Saladin and Turanshah thirty years earlier.