Yes, because they remind us of our past. If we take them down, its as if were trying to forget or erase our history. If we are not educated on history, then we are doomed to repeat It. Germany rebuilt some of its concentration camps as a reminder for their history and that it was a bad thing.
Despite Britain being relatively small country it manged to become the largest empire the world has ever seen, controlling territories on all continents in the world except for Antarctica. The reasons behind the British success were multiple, but all related with the high level of development. The British were the ones that invented and started the industrialization, which made them economic superpower. They managed to create lot of new inventions, which helped them a lot in making their military much more advanced, having superior weaponry, and equipment. Also, this empire managed to become a political superpower as well, using the politics in its advantage and being able to easily outsmart the others.
911 happened on September 11, 2011. Terrorists crashed planes into the Twin Towers in New York. It was a terrible tragedy and many lives were lost.
In North America in the parts north of the present day Mexico, the First Nations had climatically a more hostile environment to deal with than their counterparts in the now Mexico and Mesoamerica and South America. The winters on the Great Plains and in the now Canadian north were harsh and did not favor large populations to develop (with some exceptions like in British Columbia, Canada which had a mild climate and in which 100's of 1000's of First Nations lived). So the mainly plains Indians had a nomadic existence following the game and fish and so had a more egalitarian less centralized leadership than their counterparts to the south. In Mexico, Mesoamerica and South America, the climate was generally less harsh, and fairly large scale agriculture was practiced and the people were more sedentary and political power was held in the hands of rulers who though they had henchmen, tended to be all-powerful, though the Incas for example had a quite equitable system of compulsory labour for public works and mines, allowing time for the participants to work their own fields to sustain their families.
