Anarchism, reunification or pan-nationalism are sometimes used to justify and legitimize expansionism, but only when the explicit goal is to reconquer territories that have been lost, or to take over ancestral lands.
Theories of expansionismEdit
Soviet economist Nikolai Kondratiev theorised that capitalism advances in 50-year expansion/stagnation cycles, driven by technological innovation. The UK, Germany, the USA, Japan and now China have been at the forefront of successive waves.
This section needs expansion with: more historical examples. You can help by adding to it. (November 2017)
The militarist and nationalistic reign of Czar Nicholas I (1825–1855) led to wars of conquest against Persia (1826–1828) and Turkey (1828–1829). Various rebel tribes in the Caucasus region were crushed. A Polish revolt in 1830 was ruthlessly crushed. Russian troops in 1848 crossed into Austria-Hungary to put down the Hungarian revolt. Russification policies were implemented to weaken minority ethnic groups. Nicholas also built the Kremlin Palace and a new cathedral in Saint Petersburg. But Pan-slavism ambition led to further war with Turkey (the Sick man of Europe) in 1853 provoked Britain and France into invading Crimea, and Nicholas died, supposedly of grief at his defeat. 
The German Second Reich (1871–1918) underwent an industrial revolution under Bismarck, who also reformed and expanded the army. Poles and Catholics were persecuted. Colonies were acquired in Africa and China. In 1890, Kaiser Wilhelm II dismissed Bismarck and resolved to build a world-class Navy, which led to an arms race with Britain and thence to World War One. 
From 1933 the Third Reich under Hitler laid claim to the Rhineland, the Sudetenland, unification (Anschluss) with Austria in 1938, and the whole of the Czech lands the following year. After war broke out, Hitler and Stalin divided Poland between Germany and the USSR. In a Drang nach Osten aimed at achieving Lebensraum for the German people, Germany invaded the USSR in 1941. 
Colonialism, a form of expansionism is the policy of a nation seeking to extend or retain its authority over other people or territories, generally with the aim of developing or exploiting them to the benefit of the colonizing country. The European colonial period was the era from the 15th century to the mid-20th century when several European powers had established colonies in the Americas, Africa and Asia.
Expansionist nationalism is an aggressive and radical form of nationalism that incorporates autonomous, patriotic sentiments with a belief in expansionism. The term was coined during the late nineteenth century as European powers indulged in the 'Scramble for Africa' in the name of national glory, but has been most associated with militarist governments during the 20th century including Fascist Italy, Nazi Germany, the Japanese empire, and the Balkans countries of Albania (Greater Albania), Bulgaria (Greater Bulgaria), Croatia (Greater Croatia), Hungary (Greater Hungary), Romania (Greater Romania) and Serbia (Greater Serbia).
The People's Republic of China is expanding its operations and influence in the South China Sea, claiming possession of disputed offshore islands in the search for oil and gas. A major instrument of influence is the Belt and Road Initiative.
Russia's behavior threatens the integrity and existence of NATO member states and Russia's non-NATO neighbors. The events associated with Russia are: the 2008 Russo-Georgian War and Russia's occupation of South Ossetia and Abkhazia; the Russian military intervention in Ukraine, which began in 2014 with the Annexation of Crimea and the War in Donbass; and the military intervention in Syria.
The United States is seen to be using its power to expand its influence. Criticism is meted out for large-scale events (wars); for expressing support in favor of opposition groups, and for aiding the rebel groups' aspirations to remove governments. A war in Afghanistan was begun in response to the 9/11 attacks; despite opposition by traditional allies such as France, a war in Iraq was declared based on the inaccurate information of Iraq hosting weapons of mass destruction. No weapons of mass destruction were ever found, however a controversial oil law was passed through American influence, largely privatising the valuable commodity of oil to foreign companies. 
The influence of the United States extends to: embargoing countries such as Cuba; building military bases around the world, especially in the Arab countries of the Persian Gulf; supporting opposition groups in Libya and Syria during the Arab Spring and the Syrian Civil War; implementing sanctions against the leaderships of countries Venezuela, Russia, and Iran; deploying its navy in the South China Sea, widely seen as a way to counter Chinese claims in the South China Sea.
In recent times, the United States is also seen to be asserting its dominance economically. Faced by a rapidly-internationalising Renminbi and a growing eurozone, the United States is using the global dominance of the US dollar in worldwide trade to indiscriminately sanction NATO allies such as Turkey, as well as rival countries such as Russia, Venezuela and Iran; using protectionist measures against traditional allies and fellow WTO-members, Canada, Mexico, and the European Union; and initiating a major trade war with economic rival China.
In the nineteenth century, theories of racial unity such as Pan-Germanism, Pan-Slavism, Pan-Turkism and the related Turanism, evolved. In each case, the dominant nation (respectively, Prussia, Russia and the Ottoman Empire, especially under Enver Pasha,) used these theories to legitimise their expansionist policies.
In popular cultureEdit
George Orwell's satirical novel Animal Farm is a fictional depiction, based on Stalin's USSR, of a new elite seizing power, establishing new rules and hierarchies, then expanding economically while compromising their ideals; while Robert Erskine Childers in The Riddle of the Sands portrayed the threatening nature of the German Second Reich. Elspeth Huxley's novel Red Strangers shows the effects on local culture of colonial expansion into sub-Saharan Africa.
- The Muqadimmah, 1377, pages 137-256
- Orlando Figes, Crimea, Penguin, 2011, chapter one
- Allan Mallinson, '1914; Fight the Good Fight', Bantam Press, 2013, chapter two
- Sebastian Haffner, The Meaning of Hitler, Phoenix, 2000, chapters 2,3 and 4
- Colonialism, Webster's Encyclopedic Unabridged Dictionary of the English Language (1989 ed.) p. 291.; Colonialisme, Nouveau Petit Robert de la langue française (1993 ed.), p. 456.
- Simon Tisdall, 'Vietnam's fury at China's expansionism can be traced to a troubled history', The Guardian, 15/5/2004
- Tim Arango, 'Iran Dominates in Iraq after US 'handed the country over, The New York Times, 15/7/2017
- Walker, Peter (2015-02-20). "Russian expansionism may pose existential threat, says NATO general". The Guardian. Retrieved 2018-10-04.
- Orlando Figes, Crimea, Penguin, 2011, p.89