Concerning relations with the US, although Diệm admitted the importance of the US-RVN alliance, he perceived that the US's assistance to the RVN was primarily serving its own national interest, rather than the RVN's national interest. Keith Taylor adds that Diệm's distrust of the US grew because of its Laotian policy, which gave North Vietnam access to South Vietnam's border through southern Laos. Diệm also feared the escalation of American military personnel in South Vietnam, which threatened his nationalist credentials and the independence of his government. In early 1963, the Ngô brothers even revised their alliance with the US. Moreover, they also disagreed with the US on how to best react to the threat from North Vietnam. While Diệm believed that before opening the political system for the participation of other political camps, military, and security matters should be taken into account; the US wanted otherwise and was critical of Diệm's clientelistic government, where political power based on his family members and trusted associates. The Buddhist crisis in South Vietnam decreased American confidence in Diệm, and eventually led to the coup d'état sanctioned by the US. Ultimately, nation-building politics "shaped the evolution and collapse of the US-Diem alliance". The different visions in the meanings of concepts – democracy, community, security, and social change – were substantial, and were a key cause of the strains throughout their alliance.