OP here
>>2
Thank you! I've never taken any Japanese classes so hearing that made me glad. Here's the (painfully literal) English translation of what I intended to convey (the things in the square brackets are not in the original text, just trying to make it more smooth and logical for the reader):
The Africa of a certain age
In the latter part of the 19th century the large countries of Europe went to Africa, divided that continent, [which ushered in] the beginning of the colonial era. Before that, Portugal and the Netherlands explored various parts of Africa, establishing new colonies[,] especially in Southern and Western Africa. Even though, at that time, the Africans were a primitive people [i.e. not technologically advanced enough to be able to resist a European invasion], the Europeans could not advance deep into the inland [of Africa]. That was because of tropical diseases, the difficult terrain, et cetera.
>>6
Oh, your comment was very helpful. I've been doing something like that, like going to Amazon.co.jp and reading some stuff using the "なか見!検索" feature, although reading Japanese when there are so many characters you don't know (and when do know them, the combinations are not familiar) is frustrating.
As for the style, I was trying to mimic the Japanese literary style I've seen on e.g. Amazon and Wikipedia (dropping the copula is a part of it). I don't know if it's a good style to use, though.