How to answer - 3 key words/ phrases: Extent: Asking you to pass judgement. Reagan the cause: Gives you a factor to evaluate/ compare to others. End of the Cold War: Provides direction to the question for evaluating factors.
The word 'extent' means there must be at least some prioritisation of factors in your answer. To gain access to higher marks, you must show WITH EVIDENCE that the factors are interlinked and dependent upon each other, even if one in particular stands out. To access the highest marks, you should aim to put forward a coherent, nuanced argument for the end of the Cold War, whilst demonstrating, with evidence, that that the argument you've put forward is more effective than other (reasonable) points of view at explaining historical events. This can be achieved by explicitly discounting alternative interpretations throughout the essay.
Overall argument: To a quite a far extent, although Reagan did not have as big a role as Gorbachev in the process. Reagan was important for the end of the Cold War because of his military and political pressure on the USSR and more importantly, willingness to negotiate. Also, this argument must be placed within a bigger historical context of the declining USSR economy and the failure of the broader Communist ideology, particularly among the European satellite states. (This decreases the importance of Reagan's individual role).
Example first paragraph: Points for Reagan as most important: Anti-communist policies and rhetoric of 'Evil Empire'. Increased military spending which pressurised USSR: 53% increase in US defence spending (1981). Implementation of the Reagan Doctrine (militarised counter revolution) in Nicaragua, El Salvador, Grenada, Afghanistan. Critiques of Reagan as most important: From 1982-4, Reagan’s uncompromising stance failed to extract concessions from Andropov. Indeed the USA’s confrontational strategy merely prolonged the Cold War by hardening Soviet resistance. Reagan’s and Bush’s policy of constructive engagement with Gorbachev after 1985 produced much more significant results (for example the INF and START treaties). Underestimates the role of other factors in ending the Cold War, such as Gorbachev’s ‘New Thinking’, the long standing internal Soviet problems and growing popular discontent in Europe.
Other paragraphs: Importance of Gorbachev e.g. perestroika and glasnost (Critique: Gorbachev was somewhat forced into this position because of the failing Soviet system). Economic problems of the Soviet Union e.g. the economy was 50% smaller than the US. (Critique: cannot overemphasise this point because Reagan's overspend strategy had little effect between 1981-5. No real change in Soviet behaviour until Gorbachev and Reagan being willing to talk). 'People Power' - instability in Eastern European satellite states showing popular desire to move away from Soviet system. E.g. Wall comes down in East Germany (1989), Solidarity win democratic elections in Poland. (Critique: flourishing of popular will was only enabled because Gorbachev abandoned the Brezhnev Doctrine, suggesting Gorbachev had a more significant role than Reagan).