Hello Ham!
Its really great to hear from you again. You've been absent far too long. As always, excellent input, and as you point out, the presence of Islamic broadswords in Egypt certainly maintained the sword form that was ideal for the proto-kaskara in the Sudan. In Yucel, the Mamluk blades certainly do represent the blade forms prior to and through the crusades. It would not be surprising to find Mamluk swords with medieval blades, as those shown in Yucel, yet it seems uncertain as far as Sudanese kaskara are concerned. I believe at least one of Sultan Ali Dinar's blades is claimed to have a medieval blade, but the sword illustrated in Tony North's "Introduction to Islamic Arms" (V&A 1985)according to him is now in a private collection and inaccesible (p.30b, heirloom blade). The other photos of kaskaras have 19th c. and 17th c. blades. As you have noted there are coats of mail which have some early lineage in Mamluk holdings.
What you say is brilliantly worded, "...the much later influx of European trade blades to the Sudan simply served to supply a form which was retained in culturally conservative areas". Exactly !!!! Therefore the kaskara itself did not evolve from the swords of the crusaders, but remained the Arab broadsword form culturally in place from even prior to those campaigns. In later times, with the increased advent of trade blade commerce, certain European influences were imbued in quillon shapes and especially in blade features and markings, that evolved into the familiar kaskara types of the 19th-20th c.
It would seem that in earlier times, not all warriors had swords as these were expensive, the same as it was for European forces. While there may have been massive numbers of rank and file, those arms with swords were likely to have been proportionally smaller numbers. Certainly by the later period when commercial imports of trade blades increased, there would have been equally increased availability to arm growing numbers of warriors, and the more generic form that became the kaskara became established as an indiginous form with Sudanese tribes.
It seems interesting that, as you mention, the sword blade producing centers from medieval times such as Cairo, Yemen and others all but ceased producing blades and gave over to the stream of foreign blades, especially from Germany. By the 18th century, as noted, even the Omani swords were mounted with German blades.
Thank you again for posting on this Ham, hope you stay with us!!!
All the best,
Jim