For those who want to help, my suggestion is to take the eight Mahayana precepts and to recite as many Chenrezig mantras—OM MANI PADME HUM—as you can, with strong prayers to Chenrezig, praying for loving kindness to be generated in the minds of everyone, especially those who have caused this harm. You can also pray for their minds to change, to stop the thought of giving harm to others, especially those in the USA, and pray to have much peace and happiness here and in the rest of the world—as much happiness as possible. You can visualize beams of nectar emitted from Chenrezig, entering everyone in the USA, especially those who have died or have been hurt, and also entering everyone in the world, purifying all the pain, sicknesses, and negative thoughts of harm. Purify all the suffering, including one of the shortcomings of samsara: war. War is just one of the vast sufferings of samsara. Then, of course, practice this while meditating on bodhicitta. Without question, that is very important.
However, these practices are also good for you to do for yourself. Without war, cancer and so on, death will still come, and can come at any time. There is the war within our own mind, the disaster with the elements in our bodies, and, of course, there is karma. Delusions and karma are the cause of death—as long as delusion and karma exist, we won’t be able to overcome death. We will always have to go through the cycle of death and rebirth. Nobody has ever lived without dying.
Of course, it is impossible to overcome death and rebirth without Dharma, which means the end of delusion and karma. This means correctly practicing the Dharma yourself. This way you become free of death and suffering forever, and achieve everlasting happiness.
Preventing war, so that you never experience it again, comes down to Dharma, realizing emptiness, and developing the wisdom that eradicates the root of samsara: ignorance. This ignorance causes all the rest of the vast amounts of suffering.
Besides these practices, there are pujas that can be performed that take many days. They are practices to protect against the dangers of earthquakes, floods, and other such obstacles, including war. These methods definitely work against these obstacles, but they need to be done for a long time, and they need to be done by pure practitioners, who have been living a pure life with spiritual attainments. This gives more weight to pacify such obstacles. Of course, when karma has already ripened, it is much more difficult to stop. There is more opportunity to change the karma that has not yet ripened.
Bluntly speaking, at this present time it is best for us to perform strong refuge practice, and purify the negative karma of doing harm to others. In general, to prevent war in this situation, it is good for us to practice strong refuge, to practice and pray for peace. With refuge, it is good to do the prayer for preventing war, composed by the great yogi and mahasiddha Tang Tong Gyalpo, which I am translating this afternoon and will send to those who sincerely want to prevent war in the future.