The link doesn't load for me, it shows an error page. Thankfully the archive has the text in question.

Interesting run-down of the history of the expansion of the language. I must admit that I know practically nothing about Africa's linguistic landscape (specially not for modern languages!), so for me it was highly informative.

But in the mid-19th century, as demand for ivory and enslaved people expanded, local trade routes in central Africa became incorporated into a global network centred around the Indian Ocean.

This reminds me Nahuatl and Tupi in the Americas - due to colonisation they also expanded a bit, over other local languages. But unlike Swahili their expansion was short-lived (eventually the Iberian crowns enforced Spanish and Portuguese).

I also recommend people who are interested in the language to give the Swahili grammar Wikipedia page a check, IMO it's fascinating.