We present a detailed study on the effects of applied hydrostatic pressure on the magnetoresistance in doped LaMnO3 at fixed doping level. In all cases, the application of external pressure monotonically increases the Curie temperature. This is compared with the application of "internal" pressure, which is varied by substituting different rare-earth ions for La. Both effects can be understood in one simple picture that relates the structural modifications to the variation of the Mn-Mn electronic transfer integral. Thus a general phase diagram has been derived with the transfer integral as the implicit microscopic parameter dominating the magnetic and transport properties of doped LaMnO3.