:::1 . Well compulsion is bad b/c it takes away your freewill to chose . I dont think God would want somebody to be forcely converted to accept his divinity . He is needless & self sufficient .  

 :::2 . The rida wars happened b/c it was right in the middle of Arabian peninsula . Its very dangerous to have organised & armed people who dont accept your leadership , inside your land . Some of them asked for help from outside , some of them attacked muslims on regular basis , some just wanted to be exempted from Zakat ( It is important to know that Islam only imposes Zakat on muslims as a tax , that is very necessary for the poor ), Some of them claimed to be prophets , & were amassing arms, money & man power to attack Makkah/medina . 

 ::::Its worth while to mention that the medinans/makkans accepted Islam by their own choice . After the defeat of Quraish , there were so much delegations from all over the region to accept Islam ( by their own freewill ) that the year is called san-al wofood ( the year of delegations ). 

 :::3 . Well ....this is a difficult one . Mainly b/c this problem was encountered only in India , & even in India there arnt much buddhists . You might find the books by some scholars in India ,  one very well known scholar hasbeen Abul Kalam Azad .Hs studied the hindu/buddh scriptures & practices for a long time . He said that the non-abrahamic faith R alo divine . There isnt any thing said by Ram , Krishna or Buddha that is against core Islamic beliefs . Secondly there R many prophecies in these scriptures about Muhamad  , so they cant be human made . And so people following these religions should be considered as people of the book , not pagans .  

 :::There R many scholars who say that the word Dhul Kifl used in Quran is not Ezkeel but Buddha . Because the word Dhul means having/belonging , & Kifl is actually arabianised form ( there is no P sound in arabic ) of Kipl ,  or kipl vastav. So the word Dhul-Kifl means belonging to Kipl Vastav . Also in another verse God has sworn by four very honourable things . Makkah ( associated with Muhammad), Mount of Sina ( Associated with Moses ), olive ( associated with Jesus ), & fig ( supposed to be associated with Buddha ).  

 :::This is not accepted by all scholars though , but well , accepted by many . Main reason behind non-acceptance is that these things arnt explained clearly in Quran , the political conflicts b/w hindus & muslims , & b/c when muslims came to India ... U can say that the soul of Islam wasent that much strong . Otherwise there was a possibility that like zorasterans , buddhists/hindus would also havebeen declared people of the book . 

  
 :::Gren , Afghanistan has not been a country for like 30 years .Different parts of it havebeen ruled by Pushtoons , Uzbeks, Tajiks, Turkmens, Persian influenced , Soviets , & now America . If some forceful conversion is happening ( & I dont think it is ) , it will be some groups of people , who , well R illeterate in Islam . The country has been in war from 1978 , how can there be any education there ??