In lay man’s terms, the Critical Date was the point in time at which the material facts of a dispute would already have occurred. After that date, actions taken by parties to the dispute could no longer affect the issue. The Critical Date was not just terminal, it was exclusionary. Events that occurred before the Critical Date were the right-creating facts, they had substantive value, whereas events that occurred after that date had only evidentiary and probative value.

Britain argued in the Minquiers and Ecrehos Case, I.C. J . Reports 1953, p. 47 that:

‘…the theory of the critical date involves…that, whatever was the position at the date determined the critical date, such is still the position now. Whatever were the rights of the parties then, those are still the rights of the parties now. If one of them then had sovereignty, it has it now, or is deemed to have it. If neither had it, then neither has it now. The whole point, the whole raison d'etre, of the critical date rule is, in effect, that time is deemed to stop at that date. Nothing that happens afterwards can operate to change the situation as it then existed. Whatever that situation was, it is deemed in law still to exist; and the rights of the parties are governed by it.’

The Critical Date Law was usually invoked when there was a sovereignty dispute between two States regarding a piece of territory. It was used to determine to which of the two claimants the disputed territory belonged. It was invoked to establish historic title and to aid in the establishment of a good root of title to territory. The Critical Date Law has been very widely employed in international law; the following were examples.

The Pulau Ligitan and Pulau Sipadan case [Indonesia/Malaysia] ICJ Reports 2002, p. 682, para. 135): 

‘The Court further observes that it cannot take into consideration acts having taken place after the date on which the dispute between the Parties crystallized unless such acts are a normal continuation of prior acts and are not undertaken for the purpose of improving the legal position of the Party which relies on them.’

The Territorial and Maritime Dispute between Nicaragua and Honduras in the Caribbean Sea (Nicaragua v. Honduras) ICJ Reports 2007, p. 36, para. 117: 

‘[T]he significance of a critical date lies in distinguishing between those acts performed à titre de souverain which are in principle relevant for the purpose of assessing and validating effectivités, and those acts occurring after such critical date, which are in general meaningless for that purpose…Thus a critical date will be the dividing line after which the Parties' acts become irrelevant for the purposes of assessing the value of effectivités.’

Could the ‘Critical Date Law’ enable the Yorubaland to reclaim its sovereignty from Nigeria? The relevant facts were as follows:

1.     The Yorubaland for thousands of years existed as an independent sovereign nation.

2.     On 23 July, Britain signed a ‘favoured partner’ Treaty with the Yorubaland which recognised the sovereignty of the Yorubaland. 

3.     On 16 June 1890, the Treaty was ratified by the Queen and simultaneously by the Alaafin, and on that date, the Treaty was made operational by the payment of stipend to the Alaafin. 

4.     On 27 May 1899, Britain, without consultation with its treaty partner, proclaimed sovereignty over the Yorubaland by the means of a ‘protectorate’. 

5.     On 22 November 1913, Britain , again without consultation with the Alaafin, incorporated the Yorubaland into the colonial State of Nigeria.

6.     On 1 January 1914, Britain, also without consultation with the Alaafin, proclaimed the amalgamation of the Yorubaland with others. 

7.     The 1888 Treaty was a non-cession Treaty, and the Yorubaland did not transfer its sovereignty to Britain. 

8.     Clauses 6 and 7 of the 1888 Treaty had enabled consultation between the parties, as and when necessary; Britain did not make use of these clauses.

According to the facts, 16 June 1890 was the ‘Critical Date’ in this instance. The right-creating facts occurred prior to 16 June 1890. It was on that date that the Queen and the Alaafin ratified the 1888 Britain-Yoruba Treaty. The position on that date was that the Yorubaland was an independent sovereign State with rights and obligations just like any other independent State on earth, including Britain itself. According to the ‘Critical Date Law’, nothing that happened after that date, that is to say, after 16 June 1890, ‘can operate to change the situation as it then existed’. The existence of the Yorubaland as an internationally recognised State was consolidated on that 16 June 1890. Subsequent incorporation of the Yorubaland into Nigeria therefore was a nullity; it could not change the status of the Yorubaland as a sovereign State. International law thus entitled the Yorubaland to reclaim its sovereignty from Nigeria.

The Yorubaland existed as a State for centuries before Britain created the colonial State of  Nigeria. As a matter of law, therefore, the Yorubaland had the priority of importance, that is, precedence, over Nigeria. The territorial integrity of the Yorubaland took precedence in international law over the territorial integrity of Nigeria because that of the Yorubaland had been established first. In other words, Nigeria’s continuing treatment of the Yorubaland as if it were not an independent State in its own right, was continuing the illegalities that had been wrought on the Yoruba people by the ‘imperialists’.