PERSONALITY matters, as personality shapes ambition and policy preference. The personalities that matter most on the subcontinent are India’s prime minister and Pakistan’s chief of army staff.

Prime ministers Lal Bahadur Shastri and Morarji Desai were disinclined to advance India’s nuclear weapons programme, as was Vikram Sarabhai, the head of India’s Atomic Energy Commission. Their successors thought differently about the bomb, and India now has a nuclear deterrent.

A civilian, Zulfiqar Ali Bhutto, jump-started Pakistan’s nuclear weapons programme after Pakistan’s disastrous 1971 war with India. After his demise, Pakistani decision-making relating to the bomb has been the province of the army chief and a few, trusted advisers.

In the world’s largest democracy, decisions on national security also rest on a remarkably small number of votes. As V.R. Raghavan has written in the Nonproliferation Review, there has been a shift in Indian decision-making “from a collegial and consensus-based process to decisions arrived at by a small group of individuals based in the prime minister’s office”.

Partly for this reason, Kanti Bajpai has worried in Inside Nuclear South Asia that a future Indian government led by a more assertive leader of the Bharatiya Janata Party might be more inclined to resume nuclear testing or to pursue a more bellicose approach to Pakistan. A novice Congress party leader might also seek to prove his or her mettle by being more hawkish towards Pakistan.

A surprisingly diverse group of military officers have risen to become chiefs of army staff in India and Pakistan, in part because promotion to the top job is usually, but not always, based on time in service. When longevity dictates promotion, personalities will vary and surprises can result.

Pakistani political leaders have also been surprised when they skipped down the seniority ladder to pick army chiefs, as Zulfiqar Ali Bhutto (Ziaul Haq) and Nawaz Sharif (Pervez Musharraf) learned to their subsequent regret.

Likewise, in a country where civil-military relations are badly skewed, it is usually unwise for Pakistani political leaders to extend active duty service for their army chiefs. The book of political expediency in Pakistan typically does not have happy endings.

When risk-taking personalities become army chiefs during the tenure of weak, uncertain, or unseasoned prime ministers, crises usually follow. Rajiv Gandhi was not paying close attention when K. Sundarji planned very large-scale, multi-staged exercises in 1986-7. Some believe that the Brasstacks exercises were designed to prompt a war with Pakistan before it acquired nuclear weapons.

A crisis in 1990 was also sparked in part by large-scale military exercises, this time designed by Mirza Aslam Beg at a time when two weak prime ministers, Benazir Bhutto and V.P. Singh, held office. The Kargil crisis was abetted by Nawaz Sharif’s disinclination to ask very hard questions of his military briefers and his inability to put the brakes on Musharraf’s plan for an audacious land grab across the Line of Control in 1999.

The doyen of Indian strategic analysts, K. Subrahmanyam, wrote that “changes in army chiefs of staff in Pakistan are as important as changes in heads of government”. Subrahmanyam’s reasoning remains unassailable, since effective command of Pakistan’s nuclear arsenal rests in the hands of Pakistan’s chief of army staff.

The next combination of a weak prime minister and a bold army chief is more likely to occur in Pakistan than in India. The last Indian army chief slightly reminiscent of Sundarji was Gen S. Padmanabhan who, like Sundarji, wrote fiction based on military plans and who chafed at the bit to “sort out” Pakistan.

After an attack on the Indian parliament in 2001 carried out by extremists based and trained in Pakistan, Padmanabhan was kept firmly in check by Prime Minister A.B. Vajpayee. Prime Minister Manmohan Singh appears to have been much less inclined to consider a military response after the 2008 attacks on iconic targets in Mumbai, again carried out by Pakistani extremists.

This track record does not tie the hands of a future Indian prime minister. But it is notable that two veteran politicians representing coalition governments across much of the Indian political spectrum have held tight reins on the Indian military despite severe provocations.

These mass-casualty assaults were directed against targets that extremists within Pakistan find most objectionable — India’s secular democracy, economic growth and cosmopolitanism. The attacks backfired, steepening Pakistan’s decline while advancing India’s standing, partly because Indian prime ministers placed a higher priority on maintaining economic growth than on waging war with Pakistan.

As noted above, New Delhi’s future restraint after severe provocations is not foreordained. If New Delhi strikes back, the Indian army chief is unlikely to be in the driver’s seat; he will be following orders. In contrast, Pakistani army chiefs are disinclined to take orders from civilians, except ones they agree with.

The writer is co-founder of the Stimson Centre in Washington, DC, and author of Crises in South Asia: Trends and Potential Consequences (2011).