Peacekeeping Mission.

XX was a XX of XX. His mandate has been shortened{or abbreviated, curtailed} due of to* an air crash while he was on a mission. He is recognized for having laid the foundation stones of for a XX peacekeeping mission.

50th Fifty** years after his death, XX paid his tribute to whom he considered as to be an inspiring man. XX underscored the XX's*** distinguished way of work of XX. He evoked his the**** strong sense of diplomacy and the convictions***** of this principled man. As XX said: he always acts in congruence with {or "in accordance with"} what he believes. {or "he always acts according to his beliefs"}

*We always use the locution "due to" or "because of".

**When a number is the first word of a sentence, we don't use the numerical.

*** I'm assuming that this XX is not the same as the XX in the beginning of the sentence.

****It reads a little awkward to have a possesive ("his") then mention the object ("this principled man") like this. It reads better to say either "He evoked his strong sense of diplomacy and conviction." or "He evoked the strong sense of diplomacy and conviction of this principled man."

*****When we talk about a person's conviction, it's always just singular. Only when we have several people would we say "their convictions".