What is the ruling of Islamic law regarding the recovery of agricultural land that has been possessed for over 20 years, then seized by another person during the former regime, and now, after its collapse, the original possessor wishes to reclaim it, knowing that there are witnesses to his prior abandonment of it and his renunciation of subsequent reconciliation agreements?

It is not clear whether the orchard belongs to the questioner or not. The issue of possession is not a valid argument if there is evidence that the possessor is an usurper or a trustee of what is under his possession. It is also not clear whether the person who disputed with the questioner claims ownership of the orchard or intends to usurp it. The way to resolve such disputes is by resorting to legitimate judicial ruling or by amicable settlement. The questioner is warned against killing a Muslim or committing aggression, for a believer is at ease concerning his religion as long as he does not shed unlawful blood.