Mahapuranas & Upa-Puranas
The Puranas recognized as ancient  and comprehensive are called MahaPuranas which are eighteen in number. In course  of time as the society expanded new literature of new cults and new people came  to be called Upa-Puranas which are called as sub-divisions or supplements to  the major Puranas. Excepting a few, each of the Puranas exalts one or the other  deities like Vishnu, Siva, Sakti or Devi while subordinating the others. This  is more with a view to attract the focus of the devotee than to create any  sectarian rivalry; but common people do not appreciate the genius of the Vedic  religion and sectarian conflicts do take place on account of their restricted interpretation.

Place of the Bhagavatam
Srimad Bhagavatam is included in  the list of eighteen MahaPuranas wherein it finds a prominent place. There has  been a controversy whether Bhagavatam included in the list of eighteen MahaPuranas  is DeviBhagavatam or this Vishnu Bhagavatam. But many scholars speak  out in favor of the latter.

With several unknown and variable  factors involved, fixing the dates of ancient Hindu scriptures has always been  a difficult exercise. Keeping this in mind the date of Srimad Bhagavatam varies  between around 3000 B.C. (the beginning of Kali Yuga) and 8th Century A.D (the  period of Alvars of the South India) during which period there has been a  three-phase development of the text. Though tradition ascribes the authorship  of the Bhagavatam to the sage Vedavyasa, those responsible for the second and  third phases of its development have remained unknown. There are also divergent  views as to why Shankaracharya, despite his numerous works on devotion and worship,  and Ramanujacharya, despite being the leading Acharya of Vaishnavism, did not  comment or make any reference to the Bhagavatam in their extensive expositions.

The Bhagavatam as available today  has been divided into 12 Skandhas or Books, further divided into 335 Adhyayas or chapters, containing in all a little more than 14,000 slokas or  verses. However, tradition always put it at 18,000 verses.

Brahman, Bhagavan & Avatar
From the phenomenal point of  view, the Supreme Being, Brahman, is called Isvara (God) who is associated with  Maya and possessed of omnipotence, omnipresence and omniscience etc. This  transcendental Brahman is Narayana. After projecting this world and desiring to  ensure its stability, He, the Lord, Narayana, first created Prajapatis and made  them to follow the dharma (virtuous path characterized by rites and duties as  revealed in the Vedas). This dharma is the direct means to both secular and  spiritual welfare of living beings.

When after a long time, dharma  became overpowered by adharma (vice) and adharma increased owing to the  deterioration of discriminative knowledge, caused by the rise of desire in the  minds of the followers of the dharma, then Vishnu (another name of Narayana),  the prime mover took birth - as part of Himself- in the form of Krishna, the  son of Devaki by Vasudeva, for the protection of the dharma and annihilation of  the wicked. This is called the Krishna Avatara.

Avataras appear for  special reasons in special circumstances. Whenever there is much unrighteousness,  whenever confusion and disorder set in on account of unrighteousness and baffle  the well-ordered progress of people, whenever the equilibrium of human society  is disturbed by selfish, ruthless and cruel beings, whenever irreligion and  Adharma prevail, whenever the foundations of social organizations are shaken,  Avataras appear to establish Dharma and to restore peace and balance.

Avatara is a descent of  God for the ascent of man, and to keep up the harmony of the universe. The  Avatara comes to reveal the divine nature in man and makes him rise above the  petty materialistic life of passion and egoism.

Many Avataras had a  single focus, but Krishna’s achievements were multi-dimensional. Hence He is  styled as Purnavatara, or the Complete Incarnation.

He, the Lord, Krishna is called the  Bhagavan. The term ‘Bhagavan’ is defined in the Vishnu Purana (6.5.74 & 78)  as the one having Bhaga or majesty. The Bhaga or majesty is described as  sixfold Viz. 1.Lordship (Aiswarya), 2.Righteousness (Dharma), 3.Fame   (Yasas), 4.Wealth (Sri), 5.Knowledge  (Jnana), and 6.Dispassion (Vairagya). The full manifestation of  all these qualities is called Bhaga. He who is distinguished by these excellences  is the Bhagavan. He is spoken of as the One who is aware of creation and  dissolution, future prosperity and adversity, ignorance and wisdom of all  beings.

Bhagavan is ever endowed with  Knowledge, Sovereignty, Power, Strength, Valor and Formidability. He exercises  command over his own Maya which goes by the name prakriti, consisting of  three Gunas viz. sattva, rajas and tamas. Thus through his own  Maya, he appears as if embodied, as if born and as if favoring people - though  by His nature, He is birthless, changeless, the Lord of all creatures, eternal,  pure, conscious and free, the Paramatman.