Following his expulsion from Egypt over his support for Nizar, Hassan-i Sabbah found that his co-religionists, the Ismailis, were scattered throughout Persia, with a strong presence in the northern and eastern regions, particularly in Daylam, Khurasan and Quhistan.

The Ismailis and other occupied peoples of Persia held shared resentment for the ruling Seljuks, who had divided the country's farmland into iqtā’ (fiefs) and levied heavy taxes upon the citizens living therein.

[9]: 126  Hassan too, was appalled by the political and economic oppression imposed by the Sunni Seljuk ruling class on Shi'ite Muslims living across Persia.

[10]: 23  There, he made plans for the capture of the fortress, which was surrounded by a fertile valley whose inhabitants were mainly fellow Shi’i Muslims, the support of whom Hassan could easily gather for the revolt against the Seljuks.

He remained at Andej disguised as a schoolteacher named Dehkhoda until he was certain that a number of his supporters had settled directly below the castle in the village of Gazorkhan or had gained employment at the fortress itself.

Under the leadership of Hassan-i Sabbah and the succeeding lords of Alamut, the strategy of covert capture was successfully replicated at strategic fortresses across Persia, Syria, and the Fertile Crescent.

The Nizari Ismaili created a state of unconnected fortresses, surrounded by huge swathes of hostile territory, and managed a unified power structure that proved more effective than either that in Fatimid Cairo, or Seljuk Bagdad, both of which suffered political instability, particularly during the transition between leaders.

The Fortress of Alamut, which was officially called kursī ad-Daylam (كرسي الديلم, literally "Capital of Daylam") on Nizari coins,[8] was thought impregnable to any military attack, and was fabled for its heavenly gardens, impressive libraries, and laboratories where philosophers, scientists, and theologians could debate all matters in intellectual freedom.

[11] The hierarchy (hudūd) of the organization of the Nizari Ismailis was as follows: Imam and da'is were the elites, while the majority of the sect consisted of the last three grades who were peasants and artisans.

[13] As the Mongols began invading Iran, many Sunni and Shia Muslims (including the prominent scholar Tusi) took refuge with the Nizaris of Quhistan.

[14] After the death of the last Khwarezmaian ruler Jalal ad-Din Mingburnu, the destruction of the Nizari Ismaili state and the Abbasid Caliphate became the main Mongol objectives.

In 1238, the Nizari Imam and the Abbasid caliph sent a joint diplomatic mission to the European kings Louis IX of France and Edward I of England to forge an alliance against the invading Mongols, but this was unsuccessful.

Qazvin, the closest town to the valley by land can only be reached by an underdeveloped mule track upon which an enemy's presence could easily be detected given the dust clouds arising from their passage.

[10]: 27 The military approach of the Nizari Ismaili state was largely a defensive one, with strategically chosen sites that appeared to avoid confrontation wherever possible without the loss of life.

The notion of the dar al-hijra originates from the time of the Islamic prophet Muhammad, who fled with his supporters from intense persecution to safe haven in Yathrib.

During the mid-12th century the Assassins captured or acquired several fortresses in the Nusayriyah Mountain Range in coastal Syria, including Masyaf, Rusafa, al-Kahf, al-Qadmus, Khawabi, Sarmin, Quliya, Ulayqa, Maniqa, Abu Qubays and Jabal al-Summaq.

The first instance of assassination in the effort to establish an Nizari Ismaili state in Persia is widely considered to be the murder of Seljuq vizier, Nizam al-Mulk.

[10]: 29  Carried out by a man dressed as a Sufi whose identity remains unclear, the vizier's murder in a Seljuq court is distinctive of exactly the type of visibility for which missions of the fida’is have been significantly exaggerated.

[10]: 29  While the Seljuqs and Crusaders both employed assassination as a military means of disposing of factional enemies, during the Alamut period almost any murder of political significance in the Islamic lands was attributed to the Ismailis.