Looking for knowledge on Islamanisim

I am British which is not important but I need to set out what I am. Recently I took the decision to attempt to understand the world of Islam and why it appears to be in ferment. I did so because I believe that nothing in this world happens without a reason. I wanted to know why this ferment is occurring.
   
The first book I found described the development and some of the history of Islam and within it I read that when Muhammad died his position, if that's the correct term to use, Was followed by what were described by four "rightly guided"caliphs whose rule covered the period 632 to 661. I then read that three of these were assassinated which appeared to me to be rather savage bringing Islam into disrepute.

I apologise if anything I have written above offends anyone and if it does please explain to me why.

To know Islam read Quran Allah in ch 5 v 32 of Quran says if you kill a human being unless for murder or for mischief in the land means as if you have killed whole humanity if u save an innocent human being means as if you have saved whole humanity

Almost nothing is without bias, especially in something as important as a religion, perhaps even a controversial religion.

A possibly more effective tack is to read widely and work to understand the bias of each author so that you can factor that into your understanding of what to accept, what to reject, and what to consider tentative in the materials you read.

A Muslim scholar is going to write from the point of view, and the bias, of the faithful.

Someone antagonistic to Islam is going to offer a different point of view and different biases.

Be sure to check the quotes and references yourself when they disagree.

I have found both types of sources invaluable in allowing me to understand the arguments.

You also may find that you are able to use your own mind and good logic to work through towards an accurate understanding.

Very good advice from Ringer.  This is what I did also.  Read from many sources, taking into consideration the possible bias from each source. 
It is necessary to do lots of checking and cross referencing in order to create a clearer picture.  Best always to use your own mind and reach your own conclusions and not rely wholly on what another might say.