The Mamallapuram (Chennai) Summit in October 2019, an informal meeting between Indian Prime Minister Narendra Modi and Chinese President Xi Jinping, was widely seen as an attempt to build trust and de-escalate tensions following the Doklam standoff in 2017. The summit aimed to foster a strategic dialogue and manage differences. However, contrary to the spirit of Mamallapuram, the Line of Actual Control (LAC) dispute between India and China significantly deepened in 2020 with the Galwan Valley clash, followed by further standoffs in subsequent years. This paradoxical situation can be attributed to a complex interplay of long-standing structural issues and more immediate strategic triggers.

Long-Standing Structural Issues:

1. Undemarcated Border: The fundamental reason for persistent tensions is the unresolved and undemarcated 3,488 km long LAC. Both sides have differing perceptions of its alignment, leading to frequent transgressions and face-offs. Without a mutually agreed-upon boundary, incidents are inevitable.

2. Strategic Competition and Geopolitical Ambitions: Both India and China are rising powers with regional and global aspirations. Their strategic interests often clash, particularly in the Indo-Pacific region, South Asia, and the Indian Ocean. China views India's growing alignment with the Quad (US, Japan, Australia) as part of an anti-China containment strategy, while India is wary of China's expanding influence in its neighborhood.

3. Infrastructure Development: Both nations have been rapidly building military and civilian infrastructure (roads, bridges, airfields, tunnels) close to the LAC. While India views its infrastructure development as necessary to match China's existing capabilities, China perceives it as a threat to its territorial claims, especially in Aksai Chin, and its connectivity projects like the China-Pakistan Economic Corridor (CPEC).

4. Tibet Issue: China remains sensitive about India's historical association with the Dalai Lama and the Tibetan government-in-exile. Any perceived support for Tibetan separatism by India is viewed with suspicion and hostility by Beijing.

5. Water Resources: Control over transboundary rivers originating in Tibet, which are vital for India's water security, is another long-term strategic concern that adds to the underlying tensions.

Immediate and Proximate Triggers for Deepening Dispute Post-Mamallapuram:

1. India's Infrastructure Push in Ladakh: India's accelerated construction of strategic roads, particularly the Darbuk-Shyok-Daulat Beg Oldie (DSDBO) road, and other border infrastructure in Ladakh, was a significant proximate cause. China viewed this as a direct challenge to its control over Aksai Chin and its strategic interests in the region.

2. Reorganization of Jammu & Kashmir (2019): India's decision in August 2019 to revoke Article 370 and reorganize Jammu & Kashmir into two Union Territories, including Ladakh, was strongly condemned by China. Beijing viewed this as a unilateral alteration of the status quo in a disputed region, directly impacting its claims over Aksai Chin and parts of Pakistan-occupied Kashmir.

3. China's Assertiveness and 'Wolf Warrior Diplomacy': China's increasingly assertive foreign policy stance globally, often termed 'wolf warrior diplomacy,' contributed to a more aggressive posture along the LAC. Some analysts suggest China used the global distraction caused by the COVID-19 pandemic to push its territorial claims.

4. Lack of Trust and Communication Gaps: Despite high-level diplomatic engagements, a deep trust deficit persists between the two nations. This lack of trust, coupled with inadequate mechanisms for immediate de-escalation and communication during ground-level incidents, can quickly escalate local skirmishes into larger standoffs.

5. Domestic Political Imperatives: Both governments might sometimes use a firm stance on border issues to consolidate domestic nationalist sentiment and support, making it harder to compromise.

In essence, the Mamallapuram Summit, while creating a temporary atmosphere of cordiality, failed to address the fundamental divergences and strategic mistrust that define the India-China relationship. The subsequent deepening of the LAC dispute is a manifestation of these unresolved issues, exacerbated by India's infrastructure development and China's growing assertiveness, highlighting the fragile nature of peace along the disputed border. The path to lasting stability requires sustained diplomatic efforts, a clear demarcation of the LAC, and a willingness from both sides to manage their strategic competition constructively.