It is unquestionable that ideas played many important roles in historical changes; However, interests are the permanent and major causes of most historical changes. The economic difficulties in France between 1770-1789 brings out agricultural depression, which directly threaten France’s economic system. Thus, Louis XVI convened the Estates-General in order to levy more taxes more the Third Estate, unfortunately, this act brings economic burdens to the majority of French people—the Third Estate. Within the suppressing political environment and depressing economic status quo, etc. The demands for reforms intensified. In fact, the interests of Third Estate were threatened by the king, along with his administrations. Thus, accompanied by other historical factors, such as the change of the international political climate French Revolution began. Subsequently, according the quote of Lord Palmerston of England, “Nations have no permanent friends or allies, they only have permanent interest.” I believed this still can be applied to the historical changes discussion, different social classes have its own interests, different individuals have its own interests, when those interests were taken away, people will protest or even coup against the current government in order to restore their interests. Though it is undeniable ideas are the guidelines or ultimate goals for revolutions, most ideas are originated from the shift of interests. For example, John Locke proposed his ideas of Social Contract, which expresses his dissension to current governing system, since it distinct from his political standpoint. Therefore, the shifts of interests count more for historical changes.
The three words symbolized the different colors of French flag “Liberty, equality and fraternity.” Also represented the main ideas for French Revolution. Those words perfectly fit the ideas of Enlightenment Philosophes, which states the political freedom (which also means separation of government powers—ideas of Montesquieu), equal treatment to all citizens—rejecting the system of estates, and brotherhood of intellectuals, physical, moral, religious, and social development of its members, etc. By these ways, the ideas of Enlightenment thinkers formed the fundamentals of French Revolution.
The concrete evidence for French Revolution would be the conflicts between the king and the unprivileged people. When the Jacobins Club became the governing body of France, they immediately claimed the Land Acts of 1793, which gave the legal rights for peasants to gain their lands with reasonable tax system. This suggests the interests—oriented actions of newly leading French government.
As far as I’m concerned, it would be quite arbitrary to say one historical event was completely based on grand sweep or contingency; However, a combination of both sides would be appropriate. For instance, the assassination of the Austro-Hungarian heir Franz Ferdinand in Sarajevo leads to the July Crisis of 1914, which triggers World War I. However, just one single assassination of an heir is unlikely the best reason for a war to start, it has to do with European internal conflicts between empires, the struggle of old-tradition empire to keep control over the European continent—such as the British Empire, accompany with the newly-born empires—such as German Empire. The “survivor principle” for German Empire since the Chancellor Otto von Bismarck is to expand German’s territory both within the European continent, and expansion of the overseas’ colonies at the age of Wilhelm II. However, this endangers the interests of the French Empire and the Russia Empire, also brought out many problems. These conflicts accumulated as the grand sweep, and the sudden assassination of Franz Ferdinand gave those empires an opportunity to dispute those problems accumulated since last century by wars. Therefore, grand sweep needs contingency to ignite itself to change, which results in significant historical changes.