Complex sentence: It should be noted that the ambassador position at that time was different than it is today where there are ambassadors in nearly every country--in the 19th century, ambassadors were generally only exchanged between a few of the major world powers.
Split into simpler sentences: It should be noted that the ambassador position at that time was different from what it is today. Whereas ambassadors are now in nearly every country, ambassadors in the 19th century were generally only exchanged between a few of the major world powers.