有效占领制度起源于“先占”，与“发现”密切相联。但是单纯的“发现”行为仅能赋予一个国家不完全的权利，国家必须通过对该区域的有效占领行为来获得完整的主权。此外，根据时际法的要求，已经基于“先占”获得领土主权的国家，也可能由于长期缺乏有效的主权行为，而无法达到发生领土争端时的国际法对有效占领的要求，从而使该领土的主权被行使更有效主权行为且具有占领意图国家夺走。相对于国内法下土地所有权的绝对性，国际法庭在处理领土争端时，往往是将领土主权判给相对而言提出更好诉讼方案的一方。因此，为了更好地维护国家主权，各国非常有必要了解当下国际法中关于有效占领的规定。 截止至1996年的“厄立特里亚与也门案”，现代国际法对于有效占领的要求是十分明确的：在持续与和平的基础上，通过实施管辖权和国家职能，有意识地对该领土显示国家权力和权威。和平、实际、充分和持续是已经确立的有效占领制度所规定的四个要件。20世纪70年代，在中东石油危机和科技发展的作用下，海洋油气开发逐渐兴起。这引起诸多国家对于海上偏远岛屿的争夺，因为这些海岛附近的海域往往蕴藏有丰富的油气资源。而这些海岛本身，往往人迹罕至且缺乏经济价值，因此许多海岛的原主权国往往无法保持对这些海岛的“最低程度的占领”。这就给后来发现该岛附近资源的其他国家提供了夺取主权的契机。这些国家可以通过长时间持续有效的主权行为，实现对该岛的有效控制，从而获得领土主权。 “利吉坦和西巴丹案”、“尼加拉瓜与洪都拉斯加勒比海领土和海洋争端案”和“白礁岛、中岩礁和南礁案”所面对的就是这样的案情。他们反映了当今国际法下有效占领制度的新发展。本文将通过对这三个案子的分析，结合其他相关案例，重点探讨以下问题：领土主权是否可以通过“默许”的方式移转；何谓当今国际法下的有效主权行为；军事行为和油气开发行为的法律意义；地图证据在此类领土争端中的地位；主权行为的实施需要在事件和数量上符合什么要求；有权主体的越权行为是否可以归咎于国家；行使主权的意图究竟该如何证明。 在明确了当下国际法对有效占领的要求后，本文将把这些规定适用于中国南海争端中。本文的结论是：中国一直对南沙群岛实施有效控制，不存在默认导致主权移转的情形。越南提出的所谓主权行为不构成有效占领。
“Discovery” can only grant a country inchoate right of the territory. A country shall achieve complete right by effective occupation of the territory. Pursuant to the principle of inter-temporal law, the title achieved by a country through “occupation”, is very likely to be taken by another country which have exercised more effective corpus occupandi with duly animus occupandi, by the original title holder’s failure in satisfying the requirement of current international law. International tribunals always make judgment by determining which of the Parties has produced the more convincing proof of title to the other.As regulated in Eritrea & Yemen, the modern international law of the acquisition of territory generally requires that there be: an intentional display of power and authority over the territory, by the exercise of jurisdiction and state functions, on a continuous and peaceful basis. Contemporary trend in the exploitation of offshore oil and gas leads to the territorial disputes among countries towards uninhabited islands that are rich in resources. And the original title may be transferred to countries exercising more effective state power by counterparty’s acquiescence or omission. Based on the recent three cases of the ICJ, this article will illustrate the development of effective occupation under current international law, by analyzing the following issues: whether title can be transferred through acquiescence of the original holder; the legal meaning of military actions and offshore exploitation; the admissibility and probative value of map; the quantitative requirement of corpus occupandi; legal consequence of acts resulting from exceeding of authority; how to prove the animus occupandi.After applying those development in the territorial dispute between China and Viet Nam on Nansha Islands, the conclusion of this article is that: for China, there is no lose of title due to acquiescence, because it has kept effective occupation on Nansha Islands; for Viet Nam, its so-called corpus occupandi does not constitute effective occupation under current international law.
