When Buddhism first began there was only one school.
This is the history of where Mahayana started.
The Mahāsāṃghika (Sanskrit "of the Great Sangha", Chinese: 大眾部; pinyin: Dàzhòng Bù) was one of the early Buddhist schools. Interest in the origins of the Mahāsāṃghika school lies in the fact that their Vinaya recension appears in several ways to represent an older redaction overall. Many scholars also look to the Mahāsāṃghika branch for the initial development of Mahayana Buddhism.
Most sources place the origin of the Mahāsāṃghikas to the Second Buddhist council. Traditions regarding the Second Council are confusing and ambiguous, but it is agreed that the overall result was the first schism in the Sangha between the Sthavira nikāya and the Mahāsāṃghika nikāya, although it is not agreed upon by all what the cause of this split was.[6] Andrew Skilton has suggested that the problems of contradictory accounts are solved by the Mahāsāṃghika Śāriputraparipṛcchā, which is the earliest surviving account of the schism.[7] In this account, the council was convened at Pāṭaliputra over matters of vinaya, and it is explained that the schism resulted from the majority (Mahāsaṃgha) refusing to accept the addition of rules to the Vinaya by the minority (Sthaviras).[7] The Mahāsāṃghikas therefore saw the Sthaviras as being a breakaway group which was attempting to modify the original Vinaya.[8]
Scholars have generally agreed that the matter of dispute was indeed a matter of vinaya, and have noted that the account of the Mahāsāṃghikas is bolstered by the vinaya texts themselves, as vinayas associated with the Sthaviras do contain more rules than those of the Mahāsāṃghika vinaya.[7] Modern scholarship therefore generally agrees that the Mahāsāṃghika vinaya is the oldest.[7] According to Skilton, future historians may determine that a study of the Mahāsāṃghika school will contribute to a better understanding of the early Dhamma-Vinaya than the Theravāda school.
The Mahāsāṃghikas held that the teachings of the Buddha were to be understood as having
two principal levels of truth: a relative or conventional (Skt. saṃvṛti) truth, and the absolute or ultimate (Skt. paramārtha) truth.[14] For the Mahāsāṃghika branch of Buddhism, the final and ultimate meaning of the Buddha's teachings was "beyond words," and words were merely the conventional exposition of the Dharma.[15] K. Venkata Ramanan writes:[16]
The credit of having kept alive the emphasis on the ultimacy of the unconditioned reality by drawing attention to the non-substantiality of the basic elements of existence (dharma-śūnyatā) belongs to the Mahāsāṃghikas. Every branch of these clearly drew the distinction between the mundane and the ultimate, came to emphasize the non-ultimacy of the mundane and thus facilitated the fixing of attention on the ultimate.
The Mahāsāṃghikas advocated the transcendental and supramundane nature of the buddhas and bodhisattvas, and the fallibility of arhats.[14] Of the 48 special theses attributed by the Samayabhedoparacanacakra to the Mahāsāṃghika, Ekavyāvahārika, Lokottaravāda, and the Kukkuṭika, 20 concern the supramundane nature of buddhas and bodhisattvas.[17] According to the Samayabhedoparacanacakra, these four groups held that the Buddha is able to know all dharmas in a single moment of the mind.[18] Yao Zhihua writes:[18]
In their view, the Buddha is equipped with the following supernatural qualities: transcendence (lokottara), lack of defilements, all of his utterances preaching his teaching, expounding all his teachings in a single utterance, all of his sayings being true, his physical body being limitless, his power (prabhāva) being limitless, the length of his life being limitless, never tiring of enlightening sentient beings and awakening pure faith in them, having no sleep or dreams, no pause in answering a question, and always in meditation (samādhi).
A doctrine ascribed to the Mahāsāṃghikas is, "The power of the tathāgatas is unlimited, and the life of the buddhas is unlimited."[19] According to Guang Xing, two main aspects of the Buddha can be seen in Mahāsāṃghika teachings: the true Buddha who is omniscient and omnipotent, and the manifested forms through which he liberates sentient beings through his skillful means (Skt. upāya).[20] For the Mahāsāṃghikas, the historical Gautama Buddha was merely one of these transformation bodies (Skt. nirmāṇakāya), while the essential real Buddha was equated with the Dharmakāya
In the 6th century CE, Paramārtha, a Buddhist monk from Ujjain in central India, wrote about a special affiliation of the Mahāsāṃghika school with the Mahāyāna tradition. He associates the initial composition and acceptance of Mahāyāna sūtras with the Mahāsāṃghika branch of Buddhism.[31] He states that 200 years after the parinirvāṇa of the Buddha, much of the Mahāsāṃghika school moved north of Rājagṛha, and were divided over whether the Mahāyāna teachings should be incorporated formally into their Tripiṭaka. According to this account, they split into three groups based upon the relative manner and degree to which they accepted the authority of these Mahāyāna texts.[32] Paramārtha states that the Kukkuṭika sect did not accept the Mahāyāna sūtras as buddhavacana ("words of the Buddha"), while the Lokottaravāda sect and the Ekavyāvahārika sect did accept the Mahāyāna sūtras as buddhavacana.
https://en.wikipedia.org/wiki/Mah%C4...%E1%B9%83ghika
So history shows us there was a split very early in Buddhism and that what is now Mahayana and it's teachings have been around from the very beginning.
Linear Mode
