Egypt was at war with the Hittities when Tutenkhamun died. There are numerous theories about how he died & we are still unsure to this day. There are no apparent wounds or signs of disease on his mummy. He had a crack at the back of his skull. However, this has been proven to have been done following his death, maybe by the embalmers who were mummifying the king.
One theory is that he had malaria & he went riding his chariot one day, were he fell & broke his leg. Because of the malaria, his immune system was weak & he never recovered.
Tutenkhamun would have started to prepare his tomb soon after becoming a king. It was tradition that they prepared their houses for eternity as soon as they became kings.
Following the kings death, he would have been taken to a place called the beautiful house where his body was mummified. They would remove his organs & wrap them, placing them in small coffins, inside a beautiful alabaster box. This box was probably made for another king as, if you look closely, you will see that it is not the face of Tutenkhamun on the lid. They then removed his brain as leaving this would make the body decay. They then wrapped his body in bandages, the whole process took 70 days. Finally, his golden mask was placed on him. Tutenkhamun' mask is a masterpiece of pure gold & lapis lazuli.
Once the mummy was ready, a ritual called the 'Opening of the mouth' took place. The new king, Ay, touched Tutenkhamun's eyes, nose & mouth with tools to make the king able to see, smell & eat in the afterlife. His family then gathered around the tomb & shared their food with the dead king.