There are simple divorces and complex divorces and many in between. The ability of the parties to cooperate and resolve differences is the largest component to if a divorce is simple. In truth, the division of assets is legally simple: Assets which accumulate during the marriage are considered to be marital and are to be equitably split between the parties.
While this sounds simple, the practical nature is that it is often not so. Exceptions to the presumption of marital assets are: (1) premarital assets, those owned by the parties prior to marriage; (2) gifts received; or (3) inheritances received. It becomes the burden of the party seeking a non-marital offset to prove the nature of the asset.
It should be noted that it is often difficult to trace the asset to the origin. If you had a home premarital, there was likely a debt as well. If that home was sold, the proceeds may have been used to purchase a subsequent home for the parties. If that happened, some portion of the equity in the new home can be traced to the premarital interest of the first home. Conversely, if you had $5,000 in savings prior to marriage, and that money was placed into a joint account, it is very likely that money was comingled during the marriage. If more than $5,000 was put into and removed from that account during the marriage, it is impossible to trace whether the money removed was from the premarital money or the marital income.
Divorce is also about more than separation of the finances. Often divorce involves custody and parenting time with children. While there is a presumption of joint legal custody and shared time, that presumption can be overcome by considering the best interest of the children. Many longer marriages also involve spousal maintenance and support/alimony. Other disputes arise when division of assets is not clearly defined or there is sentimental value which differs from the fair market value of property.