Hey there,
Your question states: Why is little known about the Incas? One thing that I know personally is that they knew how to properly grow things. They were actually the best people who knew how to really grown there crops. But the issue was, there were a very few of these people. There little population just grew smaller and smaller. This would conclude that your correct answer would indicate to be "<span>There were so few of them"
Hope this helps</span>
<span>The sinking of the Cunard ocean liner RMS Lusitania occurred on Friday, 7 May 1915 during the First World War, as Germany waged submarine warfare against the United Kingdom who had implemented a naval blockade of Germany. The ship was identified and torpedoed by the German U-boat U-20 and sank in 18 minutes. The vessel went down 11 miles off the Old Head of Kinsale, Ireland, killing 1,198 and leaving 761 survivors.</span>
Money/income, I do believe.