A Wikipedia entry describes the life and achievements of Robert Hewsen, the extraordinary American historian and cartographer. His magnum opus is the present Atlas.

Internet Archive has the entire Atlas, divided into sections. Each section contains texts and maps about the period as well as the book's bibliography.

Introductory

Contents: Foreword, by Cyril Toumanoff; Preface; Acknowledgments; Tables of Transliteration; Symbols; Map Abbreviations; Introduction; Historical Introduction: 1. Historical Armenia; 2. The Armenian Plateau; 3. Armenia in Its Historical-Geographical Setting; 4. Orography; 5. Mt. Ararat; 6. Hydrology; 7. Climate; 8. Vegetation.

Prehistory-2nd Century A.D.

The earliest civilizations known from the territory of historical Armenia: the Nairi states (13th-9th centuries B.C.), the kingdom of Biainili (Urartu) (9th-6th centuries B.C.), Achaemenid "Armina" (550-330 B.C.), Orontid (Eruanduni) Armenia (4th-3rd centuries B.C.), Artaxiad (Artasheshean) Armenia (180 B.C.-A.D. 14), the lesser Armenian kingdoms, the Georgian kingdoms, the kingdom of Aghuania/Caucasian Albania, and the kingdom of Commagene.

Armenia as known to the Romans (1st-3rd centuries), Arsacid (Arshakuni) Armenia in the period 63-298 and later.

4th-6th Centuries

Armenia in the 4th century, the lordly (naxarar) system, the organization of the Armenian Church, the first Byzantine expansion into Armenia (387-591), the wars for religious freedom, and the second Byzantine expansion (591-654).

6th-9th Centuries

Armenians and the Byzantine empire, the territorial expansion of the great Armenian princely Houses, the anonymous Ravenna Cosmography, Armenia according to the 7th-century geographical work called the Ashxarhats'oyts', the Arab domination: the Ummayad period (654-750), and the Arab domination: the Abbasid period (750-885).

9th-11th Centuries

Armenia in the early Bagratid period (884-962), in the later Bagratid period (962-1064), the Bagratid kingdoms in Armenia and the Caucasus, the kingdom of Vaspurakan (908-1021), Eastern Armenian kingdoms and principalities (822-1261), the principality and kingdom of Siwnik', and the third Byzantine expansion into Armenia (949-1064).

11th-14th Centuries, Eastern Armenia

Eastern Armenia under the Saljuqs/Seljuks (11th-12th centuries), under the Georgians (1199-1236), Armenia according to Idrisi's map (1156), and Armenia under the Mongol Ilkhans (1256-1335).

Cilician Armenia as a Barony (1080-1198/1199) and a Kingdom (1197-1375).

14th-15th Centuries

Armenia under Turkmen domination (1378-1502).

Armenia in the Early Ottoman-Saffavid Period (1478-1590), Armenia in the Middle Ottoman-Safavid Period (1590-1639), the Armenians in Iran, Armenia in the Late Ottoman-Safavid Period (1639-1722), the Armenians of South and Southeast Asia, and the Armenian Diaspora in Eastern Europe.

The Age of the Meliks (1678-1828), Armenia in the 18th Century, the Khanate of Iravan or Ch'ukhur Sa'd, the Russian Expansion into Caucasia (1774-1878), and Armenia in the Period of Russian and Turkish Reform (1828-1877).

19th-20th Centuries-01

This section begins with a Chronology (1878-1920), and continues with text about Modern Armenia: Armenia on the Eve of the First World War (1878-1914); the City of Constantinople; the City of Smyrna; the Vilayet of Erzurum; the Vilayet of Sivas; the Vilayet of Adana; the Vilayet of Mamuretulaziz and the Autonomous Sanjak of Marash; the Vilayet of Diyarbekir and the Autonomous Sanjak of Urfa; the Vilayet of Bitlis; the Vilayet of Van; and the Vilayet of Trabzon.

This section describes Western Transcaucasia (Russian Armenia), 1878-1914; Eastern Transcaucasia, 1878-1914; the Peoples of Caucasia; the Armenian Episcopal Sees in 1910; and the Armenian Dialects.

20th Century-01

Armenia in the First World War, 24 Oct. 1914-30 Oct. 1918; the Armenian Genocide; and the First Republic of Armenia, 28 May 1918-2 December 1920.

20th Century-02

This section begins with a Chronology (1920-2000) followed by text about Armenia in the Soviet Period (1920-1990); the Armenian Republic (Physical); Soviet Armenia: History and Administration (1920-1990); and Soviet Armenia: Economy.

20th Century-03

Contemporary Armenia: the City of Erevan; the Monastery of Ejmiatsin; the Autonomous Province of Highland Karabagh (Nagorno-Karabakh); the Nakhichevan Autonomous Soviet Socialist Republic; Armenian Historical and Cultural Sites in Western Armenia, Iran, and Eastern Armenia.

20th Century-04

This is the final portion of the Atlas and deals with the Armenian Diaspora and the Armenian Republic (to 2000). Topics: the Armenians in the Middle East; in Europe; in South America; the Armenians in the United States and Canada; the Armenian Church in North America; Diaspora Communities Elsewhere; Epilogue: the New Armenian Republic; and Conclusion.