What was the first "intervening obstacle" which hindered american settlement of the interior continent?

could you send me the choices?

music always has an important role in culture and societies, infact for example rock’n roll music has conditioned different areas of pop culture above all in the 60s. in the modern american society its role is different.

unfortunately many think about how some unfortunate events happened to the columbine high school shootings can be related to rock music just because the teenagers involved listened to this kind of music.

i think that we can valorize the change to take refuge in this genre of music to keep on in everyday life, teenagers are comfortable when they can listen to a song about a specific problem. realizing that someone else is living your personal drama too can them to feel less lonely nowadays.