A window of opportunity means a period during which a state possesses a significant military advantage over an adversary (Lebow 1984, 147). Throughout the cold war, western defense experts and intelligence had worried that the Soviet Union had a window of opportunity because of its military capability and expansionist ambition (Johnson 1983; Rush 1982/1983; Gray 1978; Pipes 1977; Mearsheimer 2001). They even feared that the Soviet economy would eventually generate greater wealth and cause a power shift against the United States. Picking up this theme, President Ronald Reagan warned that a window of vulnerability was opening, and he attempted to justify his call for new and more strategic weapons (Scheer 1982). However, the collapse of the Soviet Union and the peaceful end of the cold war proved that the Soviet Union was much weaker than the United States and was just a declining challenger (Wohlforth 1994/1995). The Soviet Union appeared to rise in the 1950s and 1960s but soon began to fall and never achieved power parity with the United States. In the economic area, the Soviet Union rarely achieved a GDP of even half that of the United States (Lemke 1997). Even in the military area, in which the Soviet Union appeared to have a relative advantage, it was not strong enough to take an offensive war against the United States and its allies (Mearsheimer 1982; Posen 1984/1985). Rather than use a so-called window of opportunity and initiate a war, the Soviet Union turned out to be so untenable that it collapsed in the late 1980s.
Also in the Korean peninsula, many scholars have argued that North Korea has had a window of opportunity and has been ready to initiate a second Korean War at any moment due to its military capability and offensive intentions (Betts 1993/1994; Levin 1990; Choi 1985; Park 1992; Izumi 1992; Oh 1990). Its numerical superiority in armed forces and some hardware compared to those of South Korea has been regarded as its general superiority in national power, and its continuous military buildup has been seen to prove its offensive intention. However, the long peace in the peninsula after the Korean War in 1950 indicates that the North Korean military threat has been overemphasized like that of the Soviet Union. North Korea has never had the material capability to be prominent over the South, and the balance of power around the Korean peninsula has continuously moved against the North (Kang 2003). In the economic area, North Korea was close to South Korea in the 1960s but quickly fell behind. The military balance has also become unfavorable to the North, both qualitatively and quantitatively. The two Koreas were in rough parity in military capability until the early 1970s, but the North began to fall behind since. North Korea still possesses more armed forces and hardware than the South, but the South's military is more efficient because it is supported by its much stronger economy. Moreover, South Korea has continuously enjoyed strong U.S. security guarantees, while North Korea lost two major patrons in Russia and China after the cold war. Considering these circumstances, what holds for the Korean peninsula seems to resemble U.S.-Soviet relations during the cold war. North Korea has been a weaker and declining challenger to the South just as the Soviet Union was to the United States, so that the North has been deterred in the same way that the Soviet Union was during the cold war.
In short, both the Soviet Union and North Korea were weaker and declining nations compared to the United States and South Korea, so that it is logically or empirically wrong to argue that such weaker states had windows of opportunity. Then why did so many scholars support the theory of windows of opportunity of weaker states? This article argues that it is largely because they give too much emphasis to the offensive intentions of weaker states and often ignore the balance of power among nations. Either explicitly or implicitly, their arguments depend on the assumption about revisionist states and imply that weaker states may attack their stronger opponents if they have revisionist aims. This article demonstrates that these arguments cannot be theoretically supported. It argues that offensive realism, which many of these arguments are theoretically based on, does assume a revisionist state necessarily manifests offensive behavior. Because a state's behavior is determined not only by what it wishes to do but also by what it possesses, a weaker state is not easily expected to behave offensively even with an offensive intention (Mearsheimer 2001). In fact, due to the power gap, the cold war ended peacefully and the Korean peninsula has enjoyed a long peace since the Korean War.
This article, however, does not conclude that simple deterrence always works for weaker states. In fact, weaker states may challenge stronger opponents, and history has demonstrated that there are a number of cases in which the weaker …