<Table> <Tr> <Th_colspan="2"> Boston Marathon bombing </Th> </Tr> <Tr> <Td_colspan="2"> Part of Terrorism in the United States </Td> </Tr> <Tr> <Td_colspan="2"> Moments after the first explosion </Td> </Tr> <Tr> <Th> Location </Th> <Td> 671--673 and 755 Boylston Street, Boston, Massachusetts </Td> </Tr> <Tr> <Th> Date </Th> <Td> April 15, 2013 (2013 - 04 - 15) 2: 49 p.m. (EDT) </Td> </Tr> <Tr> <Th> Target </Th> <Td> Boston Marathon </Td> </Tr> <Tr> <Th> Attack type </Th> <Td> Bombings </Td> </Tr> <Tr> <Th> Weapons </Th> <Td> Two pressure cooker bombs </Td> </Tr> <Tr> <Th> Deaths </Th> <Td> </Td> </Tr> <Tr> <Th> Non-fatal injuries </Th> <Td> ≈ 264 </Td> </Tr> <Tr> <Th> Perpetrators </Th> <Td> <Ul> <Li> Dzhokhar Tsarnaev (sentenced to death) </Li> <Li> Tamerlan Tsarnaev (deceased) </Li> </Ul> </Td> </Tr> <Tr> <Th> Motive </Th> <Td> Retribution for U.S. military action in Afghanistan and Iraq </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Boston Marathon bombing </Th> </Tr>

What was the motive for the boston marathon bombing