The "if history is any guide" part is an allusion to mostly alleged famous events. Like The Rape of the Sabine Women or the Trojan War. Not 30 million, just one woman missing is reason for war. Right? Or, just one male too many, if you look from the other side. But investigating this claim as a historian by looking at real events this theory becomes much less convincing.
From a population conservation or population growth perspective, unmarried males are a non problem. Women are the scarce resource here. Being pregnant, giving birth, nursing children takes time, time in which a single male can father dozens of offspring. Unmarried women have seldom caused a reason for concern, the words like spinster are testament to that. But unmarried males are seen as much more aggressive, especially when young, in this case of a hypothesis primarily due to sexual frustration.
But that is the problem of oversimplification. This is not all about sex, but it is about age, and it is indeed about frustration. Frustration stemming from a lack of a promising future perspective, and not just marital bliss, but economical as well. And whether we ask Marx or Clinton: "it's the economy, stupid!"
Let's not forget that sexual frustration is easily solved by a number of means with varying degrees of historical precedence and current success: prostitution, gay marriage, the internet, and sex-robots. More seriously but less practical one might look to Freud's theory of sublimation.
The real theory behind males waging war is the so called Youth bulge theory, first formulated by Fuller after ideas from Gaston Bouthoul and expanded by Gunnar Heinsohn:
In his theory about the "youth bulge", Heinsohn argues that an excess in especially young adult male population predictably leads to social unrest, war and terrorism, as the "third and fourth sons" that find no prestigious positions in their existing societies rationalize their impetus to compete by religion or political ideology. Heinsohn claims that most historical periods of social unrest lacking external triggers (such as rapid climatic changes or other catastrophic changes of the environment) and most genocides can be readily explained as a result of a built up youth bulge, including European colonialism, 20th century Fascism, and ongoing conflicts such as that in Darfur, The Palestinian uprisings in 1987-1993 and 2000 to present, and terrorism.
This is fully fleshed out in his book: Gunnar Heinsohn: "Söhne und Weltmacht. Terror im Aufstieg und Fall der Nationen", Orell Füssli: Zürich, 2006. (Translation of the title: "Sons and World Power. Terror in the Rise and Fall of Nations")
The main problem articulated in this theory is about attainable social status, economic perspectives foreseeably denied to aggressive young males in growing and ageing populations. Any possible sexual frustration is only added on top and plays a very small role. Since the ageing population in the case of china is more of a problem than the continued but slowing growth, this theory would be still applicable. This has not much to do with scarcity of females (Heinsohn writes that "female uteruses dictate the outcome of the next war"), aggressiveness of males ("it's in their nature, testosterone etc."). This is about how the society is organised, economically and socially.
This focus on sex in the question is rooted in structuralist theory. That can be summarised basically: Everything done in a society comes down to a certain the Exchange of women. As bad as Wikipedia does a job in describing that theory, as a frame of reference for analysis this has some merits. As a societal model of inevitability it is flawed.
Economic problems in a system of inheritance laws preferring primogenitur was for a long time solved in German states with the adage: "The first son gets the farm, the second son is sent into the clergy and the third son is sent into war."