Why did they do this to me at the airport?

i recently flew to alaska and when i was int he airport in minneapolis(MN) and the security people pulled me off to the side and asked me all these questions and then took me to a another room to search me...but im ONLY 15 years old..so why the hell would they act like im a terrorist and iv never been sent to jail or juv...and they dint let me take any carryones i ahd to have all go with the baggage.. i asked them y they did that..they said for security reasons???