Long(Plio-Pleistocene) summer monsoon records have now been produced from the Arabian Sea,South China Sea and Chinese Loess Plateau,representing both the Indian and East Asian monsoon sub-systems.All records have all been placed on the global marine benthic oxygen isotope time-scale(LR04).These Indian and East Asian records are synthesized to evaluate the timing of maximum summer monsoon circulation relative to external insolation forcing at the Earth-orbital obliquity and precession bands and to infer from these relationships,the primary internal and external mechanisms driving changes in monsoon strength at orbital time scales.Summer-monsoon records from all three locations have similar phase responses at the obliquity and precession bands indicating that the Indian and East Asian systems are tightly coupled and driven by common forcing mechanisms throughout the past 2.7 Ma.The common response among the proxy records over the past 2.7 Ma is consistent with the fact that the Indian and East Asian systems have a common energy source;the majority of moisture(energy) entering the Indian and East Asian systems comes from the southern hemisphere Indian Ocean.At the obliquity band,the phase response indicates that strong monsoons are equally sensitive to sensible heating over Asia,latent heat export from the southern Indian Ocean,and decreased glacial boundary conditions.At the precession band,the phase response indicates that strong monsoons are sensitive to latent heat export from the southern hemisphere Indian Ocean and decreased glacial boundary conditions.Model results from the fully coupled ocean-atmosphere Fast Ocean Atmosphere Model(FOAM) support this link to latent heat export. Long (Plio-Pleistocene) summer monsoon records have now been produced from the Arabian Sea, South China Sea and Chinese Loess Plateau, both of Indian and East Asian monsoon sub-systems. All records have all been placed on the global marine benthic oxygen isotope time-scale (LR04). These Indian and East Asian records are synthesized to evaluate the timing of maximum summer monsoon. external mechanisms driving changes in monsoon strength at orbital time scales.Summer-monsoon records from all three locations have similar similar responses at the obliquity and precession bands indicating that the Indian and East Asian systems are tightly coupled and driven by common forcing mechanisms throughout the past 2.7 Ma. The common response among the proxy records over the past 2.7 Ma is consistent with the fact that the Indian an d East Asian systems have a common energy source; the majority of moisture (energy) entering the Indian and East Asian systems comes from the southern hemisphere Indian Ocean. At the obliquity band, the phase response indicates that strong monsoons are equally sensitive to sensible heating over Asia, latent heat export from the southern Indian Ocean, and decreased glacial boundary conditions. At the precession band, the phase response indicates that strong monsoons are sensitive to latent heat export from the southern hemisphere Indian Ocean and decreased glacial boundary conditions. Model Results from the fully coupled ocean-atmosphere Fast Ocean Atmosphere Model (FOAM) support this link to latent heat export.