Key point: Occupying Iran would require controlling and pacifying an area the size of Western Europe.

To understand Iran, you must begin by understanding how large it is. Iran is the 17th largest country in world. It measures 1,684,000 square kilometers. That means that its territory is larger than the combined territories of France, Germany, the Netherlands, Belgium, Spain and Portugal — Western Europe. Iran is the 16th most populous country in the world, with about 70 million people. Its population is larger than the populations of either France or the United Kingdom.

Under the current circumstances, it might be useful to benchmark Iran against Iraq or Afghanistan. Iraq is 433,000 square kilometers, with about 25 million people, so Iran is roughly four times as large and three times as populous. Afghanistan is about 652,000 square kilometers, with a population of about 30 million. One way to look at it is that Iran is 68 percent larger than Iraq and Afghanistan combined, with 40 percent more population.

More important are its topographical barriers. Iran is defined, above all, by its mountains, which form its frontiers, enfold its cities and describe its historical heartland. To understand Iran, you must understand not only how large it is but also how mountainous it is.

Iran’s most important mountains are the Zagros. They are a southern extension of the Caucasus, running about 900 miles from the northwestern border of Iran, which adjoins Turkey and Armenia, southeast toward Bandar Abbas on the Strait of Hormuz. The first 150 miles of Iran’s western border is shared with Turkey. It is intensely mountainous on both sides. South of Turkey, the mountains on the western side of the border begin to diminish until they disappear altogether on the Iraqi side. From this point onward, south of the Kurdish regions, the land on the Iraqi side is increasingly flat, part of the Tigris-Euphrates basin. The Iranian side of the border is mountainous, beginning just a few miles east of the border. Iran has a mountainous border with Turkey, but mountains face a flat plain along the Iraq border. This is the historical frontier between Persia — the name of Iran until the early 20th century — and Mesopotamia (“land between two rivers”), as southern Iraq is called.

The one region of the western border that does not adhere to this model is in the extreme south, in the swamps where the Tigris and Euphrates rivers join to form the Shatt al-Arab waterway. There the Zagros swing southeast, and the southern border between Iran and Iraq zigzags south to the Shatt al-Arab, which flows south 125 miles through flat terrain to the Persian Gulf. To the east is the Iranian province of Khuzestan, populated by ethnic Arabs, not Persians. Given the swampy nature of the ground, it can be easily defended and gives Iran a buffer against any force from the west seeking to move along the coastal plain of Iran on the Persian Gulf.

Running east along the Caspian Sea are the Elburz Mountains, which serve as a mountain bridge between the Caucasus-Zagros range and Afghan mountains that eventually culminate in the Hindu Kush. The Elburz run along the southern coast of the Caspian to the Afghan border, buffering the Karakum Desert in Turkmenistan. Mountains of lesser elevations then swing down along the Afghan and Pakistani borders, almost to the Arabian Sea.

Iran has about 800 miles of coastline, roughly half along the eastern shore of the Persian Gulf, the rest along the Gulf of Oman. Its most important port, Bandar Abbas, is located on the Strait of Hormuz. There are no equivalent ports along the Gulf of Oman, and the Strait of Hormuz is extremely vulnerable to interdiction. Therefore, Iran is not a major maritime or naval power. It is and always has been a land power.

The center of Iran consists of two desert plateaus that are virtually uninhabited and uninhabitable. These are the Dasht-e Kavir, which stretches from Qom in the northwest nearly to the Afghan border, and the Dasht-e Lut, which extends south to Balochistan. The Dasht-e Kavir consists of a layer of salt covering thick mud, and it is easy to break through the salt layer and drown in the mud. It is one of the most miserable places on earth.

Iran’s population is concentrated in its mountains, not in its lowlands, as with other countries. That’s because its lowlands, with the exception of the southwest and the southeast (regions populated by non-Persians), are uninhabitable. Iran is a nation of 70 million mountain dwellers. Even its biggest city, Tehran, is in the foothills of towering mountains. Its population is in a belt stretching through the Zagros and Elbroz mountains on a line running from the eastern shore of the Caspian to the Strait of Hormuz. There is a secondary concentration of people to the northeast, centered on Mashhad. The rest of the country is lightly inhabited and almost impassable because of the salt-mud flats.

If you look carefully at a map of Iran, you can see that the western part of the

country — the Zagros Mountains — is actually a land bridge for southern Asia. It is the only path between the Persian Gulf in the south and the Caspian Sea in the north. Iran is the route connecting the Indian subcontinent to the Mediterranean Sea. But because of its size and geography, Iran is not a country that can be easily traversed, much less conquered.

The location of Iran’s oil fields is critical here, since oil remains its most important and most strategic export. Oil is to be found in three locations: The southwest is the major region, with lesser deposits along the Iraqi border in the north and one near Qom. The southwestern oil fields are an extension of the geological formation that created the oil fields in the Kurdish region of northern Iraq. Hence, the region east of the Shatt al-Arab is of critical importance to Iran. Iran has the third largest oil reserves in the world and is the world’s fourth largest producer. Therefore, one would expect it to be one of the wealthiest countries in the world. It isn’t.

Iran has the 28th largest economy in the world but ranks only 71st in per capita gross domestic product (as expressed in purchasing power). It ranks with countries like Belarus or Panama. Part of the reason is inefficiencies in the Iranian oil industry, the result of government policies. But there is a deeper geographic problem. Iran has a huge population mostly located in rugged mountains. Mountainous regions are rarely prosperous. The cost of transportation makes the development of industry difficult. Sparsely populated mountain regions are generally poor. Heavily populated mountain regions, when they exist, are much poorer.

Iran’s geography and large population make substantial improvements in its economic life difficult. Unlike underpopulated and less geographically challenged countries such as Saudi Arabia and Kuwait, Iran cannot enjoy any shift in the underlying weakness of its economy brought on by higher oil prices and more production. The absence of inhabitable plains means that any industrial plant must develop in regions where the cost of infrastructure tends to undermine the benefits. Oil keeps Iran from sinking even deeper, but it alone cannot catapult Iran out of its condition.

The Broad Outline

Iran is a fortress. Surrounded on three sides by mountains and on the fourth by the ocean, with a wasteland at its center, Iran is extremely difficult to conquer. This was achieved once by the Mongols, who entered the country from the northeast. The Ottomans penetrated the Zagros Mountains and went northeast as far as the Caspian but made no attempt to move into the Persian heartland.

Iran is a mountainous country looking for inhabitable plains. There are none to the north, only more mountains and desert, or to the east, where Afghanistan’s infrastructure is no more inviting. To the south there is only ocean. What plains there are in the region lie to the west, in modern-day Iraq and historical Mesopotamia and Babylon. If Iran could dominate these plains, and combine them with its own population, they would be the foundation of Iranian power.

Indeed, these plains were the foundation of the Persian Empire. The Persians originated in the Zagros Mountains as a warrior people. They built an empire by conquering the plains in the Tigris and Euphrates basin. They did this slowly, over an extended period at a time when there were no demarcated borders and they faced little resistance to the west. While it was difficult for a lowland people to attack through mountains, it was easier for a mountain-based people to descend to the plains. This combination of population and fertile plains allowed the Persians to expand.

Iran’s attacking north or northwest into the Caucasus is impossible in force. The Russians, Turks and Iranians all ground to a halt along the current line in the 19th century; the country is so rugged that movement could be measured in yards rather than miles. Iran could attack northeast into Turkmenistan, but the land there is flat and brutal desert. The Iranians could move east into Afghanistan, but this would involve more mountain fighting for land of equally questionable value. Attacking west, into the Tigris and Euphrates river basin, and then moving to the Mediterranean, would seem doable. This was the path the Persians took when they created their empire and pushed all the way to Greece and Egypt.