agencies. In some countries, such as Sweden, these adoptions account for the majority of cases (see above table). The U.S. example, however, indicates there is wide variation by country since adoptions from abroad account for less than 15% of its cases. More than 60,000 Russian children have been adopted in the United States since 1992, and a similar number of Chinese children were adopted from 1995 to 2005. The laws of different countries vary in their willingness to allow international adoptions. Recognizing the difficulties and challenges associated with international adoption, and in an effort to protect those involved from the corruption and exploitation which sometimes accompanies it, the Hague Conference on Private International Law developed the Hague Adoption Convention, which came into force on 1 May 1995 and has been ratified by 85 countries as of November 2011. Embryo adoption: based on the donation of embryos remaining after one couple's in vitro fertilization treatments have been completed; embryos are given to another individual or couple, followed by the placement of those embryos into the recipient woman's uterus, to facilitate pregnancy and childbirth. In the United States, embryo adoption is governed by property law rather than by the court systems, in contrast to traditional adoption. Common law adoption: this is an adoption that has not been recognized beforehand by the courts, but where a parent, without resorting to any formal legal process, leaves his or her children with a friend or relative for an extended period of time. At the end of a designated term of (voluntary) co-habitation, as witnessed by the public, the adoption is then considered binding, in some courts of law, even though not initially sanctioned by the court. The particular terms of a common-law adoption are defined by each legal jurisdiction. For example, the U.S. state of California recognizes common law relationships after co-habitation of 2 years. The practice is called "private fostering" in Britain. Disruption and dissolution Although adoption is often described as forming a "forever" family, the relationship can be ended at any time. The legal termination of an adoption is called disruption. In U.S. terminology, adoptions are disrupted if they are ended before being finalized, and they are dissolved if the relationship is ended afterwards. It may also be called a failed adoption. After legal finalization, the disruption process is usually initiated by adoptive parents via a court petition and is analogous to divorce