Why are the congo and zambezi rivers unsuitable for long distance trade

Which  was not a problem faced by farmers in the late 19th century

It can be inferred that the dramatic increase in defense spending by germany was the result of. (a) attempts by great britain to take german colonies. ( b) fear of a two-front war against france and russia (c) the need to put down a communist rebellion (d) a competition with the allies to produce atomic weapons

The roman empire created the worlds first