There have been numerous attempts to improve the relationship, notably the Shimla summit, the Agra summit, and the Lahore summit. Since the early 1980s, relations between the two nations have grown increasingly sour, particularly after the Siachen conflict, intensification of the Kashmir insurgency in 1989, Indian and Pakistani nuclear tests in 1998, and the 1999 Kargil War. Certain confidence-building measures, such as the 2003 ceasefire agreement and the Delhi–Lahore Bus service, have been successful in de-escalating tensions. However, these efforts have been impeded by periodic terrorist attacks. The military standoff following the 2001 Indian Parliament attack raised concerns of a possible nuclear war. The 2007 Samjhauta Express bombings, which killed 68 civilians (most of whom were Pakistani), was also a crucial turning point in relations. Additionally, the 2008 Mumbai attacks carried out by Pakistani militants resulted in a severe blow to the ongoing India–Pakistan peace talks.