Monogamy is the ideal human sexual relation created and sealed by God  Himself. God did not create multiple  partners for Adam. He only created one and that was Eve. I am not using  Church Dogma here but the bible. I would like to show here that Monogamy is Biblical just as  Polygyny (:  the state or practice of having more than one wife or female mate at a  time  ) is. Monogamy is God's perfect Union based on God's perfect will  while Polygyny was and is allowed based on God's permissive will. 
First, there is nowhere in African History where one was married without  a wedding-when I say this I want us to understand that weddings are  not necessarily religious in the western world. They are cultural. In  Africa, however, weddings happened to be religious because religion  permiated the entire fabric of the african world view. You cannot  divorce religion from any African activity including child birth,  naming,initiation, marriage and death. I would like any interested reader to read John S  Mbitis African Religions and Philosophies and Gehman's African Traditional Religion Abiblical perspective,  to get a glimpse of some the aspects of the african worldview I am talking about.
Weddings, before the  coming of even chritianity, were very present in Africa and marriage was only  between one man and one wife. The other wives who came in as second or  third, were but mere associations of the man with other people and no wedding was done for them. Nonetheless bridewealth was given to the newly married women's parents. The  other wives were subordinate to the first wife and they claimed nothing  over that which the first wive allowed them to have. However, children from all  wives enjoyed equal rights.
The  first instance of this type of marriage, which is also called bigamy, in  the Bible was that of Lamech in Genesis 4:19:who married two wives.  There is no where in the bible where this kind of marriage is condemned  or considered to be sin. In the New Testament, there are inferences as  to the existance of such unions in the church because if they were  non-existant, Paul would not have talked about -a man of but one wife- when he was laying down the qualifications of a leader in the church..
Second, a vital question asked here by one Harry is ;But how come our forefathers succeeded in having several wives, and even raised stable families? Success  is very relative and the criterion to measure success esopecially in family matters varies from culture to culture. The Maasai and other pastrolists for example would consider success to have thousands head of cattle, while among other communities, having many children who have good jobs and have big tracts of land would be seen as success. 
    When all is said and done there are however very many factors that allowed people  who lived in those days to manage big families with multiple wives.
 1.  Availability of economical resources, land, food, livestock etc.
2.  Political power, like your grandfather (Mumia Nabongo) who took other  people's wives just because he was a Mwami,  read King.
3. There were laid down marriage laws that governed this  institution and these laws were passed on by word of mouth from one  generation to another e.g. total respect for the first wife, the man  must provide for all the women failure to which the society would deal  with the culprit. For insatance, one could not just marry without having built a house for  the second wife and shown that he has the capability and capacity to mange two houses. 
Third, Second wives were not just taken without real reasons. Second  wives were married because either the first wife could not have  children, she was incapacitated is a way or another, the need to have  boys or girls( since it was believed that having boys or girls was the  woman's problem not the man's). The same reasons appear in the bible.
 
Lastly, the issue of making monogamy legal and polygyny or polygamy  ilegal, is a matter of the law of the land which allows a man to marry  only one wife and if one is found with two wives with two marriage  certificates then, that is a matter that has to be taken to court. Only  one marriage certificate is given to one couple. If an individual wants to marry a second  wife, then  the first must be nullified through a legal process. The Muslims marry upto four wives I  do not know if the Kenya Goverment issues four marriage certificates.