The medieval era of Iran history that lasted about nine centuries is considered as one of the most important and effective periods of this country. Conversion، the emergence of thought schools and religious sects accompanying wide political، economic، cultural، and social evolutions created deep and multilateral problems in the nation، and caused fundamental problems for its own. The main issue، in the present research، is surveying lineament of epochal problems caused by the mentioned phenomena and occurrences happened in Iran during the first to the nine centuries? and In what kind of comparatively steady historical processes does his problem find its origin? In order to reach the descriptive findings، as in historical researches، historical data were extracted from available resources; these findings، then، were employed as stuffs to model an interpretive plot. From the proofs and documents، it is deducted that during the Iran’s medial era there appeared an allied triangle of epochal problems. These problems are as follow: 1. The problem of periodic attacks of outsiders and eternal political instability، 2. The problem of conversion and consistent religious-sectary quarrels، and 3. The problem of social gaps and severity of the mosaic situation in the society. The available findings indicate that the relationship between these events and problems and the reciprocal relationships of the problems was a dialectic relationship. Consequently، there was a consistent interaction between vicissitudes and epochal problems of this era.