"The Kitab Gbunja noted that in about February 1745, "the cursed unbeliever, Opoku, entered the town of Yendi and plundered it."

   The Ya Na, Gariba, was taken prisoner.  When he was being carried to Kumasi, his nephew, Ziblim, the Chief of Nasah, interceded and redeemed him."

This source put to rest that it was Opoku Ware not Sei Kwadwo who got to Dagomba first.

Sei Kwadwo had to go and reconquer about 20 years later when Santehene Obudom had allowed things to "fall apart" a little bit...

"........After Opoku Ware death, the Muslim chronicler Al-Hajj Muhammed Ibn Mustafa in the Kitab Ghunja criticized him for harming the people of Gonja by oppressing them, robbering their property, complaining he ruled violently as tyrant and noting that people all around feared him greatly......."

The above quote also put the Gonja question to rest.  In all, Opoku Ware did expand all the way to North....before Sei Kwadwo had to do it again for reasons already stated in the comment.

And as history recorded,  the Gonjas were able to regain  their independence  after Sir Garnet had invaded Asante some 150 years later in 1874.

Suffice to say and history records that all Asantes in Gonja were put to the sword in 1874.

So much so that after almost a 120 years after Opoku Ware went to Gonja, the Gonjas still maintained the memory of his deeds through generations - about 5 generations.....and after 120 years or so, when none of Opoku Ware generation were alive, the Gonja took revenge by slaying all Asantes in their land.

Hm..

The lives of nations are long.  A generation is just figment.  

Yeah...one historian, I think Ivor, broke down the empire into three:

1. Greater Asante- made up of the original states which formed the Union.

2. Provincial Asante: Akan states under Asante i.e sharing immediate borders.

3. Annexed Asante: like Dagomba, Jasikan etc....

And yes, Provincial Asante was always rebelling....

While Annexed Asante was almost always faithful.

K Arhin: The Structure of Greater Asante, 1967.

Abstract. 

Between the years 1700 and 1820 the Ashantis of central Ghana fought a number of wars in nearly all the territories now comprising modern Ghana. 

Most interpretations of these wars have linked them with the European trade posts on the southern coast and the Muslim trade settlements in the north. The Ashanti wars were therefore either raids or attempts to open trade-routes to the trade-posts.

 These interpretations have been possible because writers have ignored the Ashanti expansionary movement before 1700, and have also been unable to interpret correctly the political significance of the institutions by which the Ashanti attempted to extend their rule into some of the conquered territories, and to integrate them into what the Ashanti conceived as 'Greater Ashanti'-a political community incorporating the conquered Akan states under the rule of the Golden Stool, the supreme stool of Ashanti. 

When, then, the pre-1700 Ashanti tradition and the introduction of Ashanti judicial, political and politico-religious institutions into some of the conquered territories are carefully considered, it becomes clear, in the writer's view, that the so-called Ashanti 'empire' should be divided into three categories of states: provinces, 'protectorates' and tributaries, on the basis of their political distance from Ashanti. The provinces-like the Ashantis mainly Akan-speaking peoples-were considered and treated as part of a Greater Ashanti 'political structure'. The 'protectorates' were treated as allies or protected peoples according as economic or political circumstance dictated. The tributaries formed the economic and manpower base of the Ashanti expansion. But it must be noted that these relationships were fluid, and fluctuated with Ashanti military and political fortunes.

 Finally, the Ashanti political experiment was halted by the British and was therefore inconclusive. The student can, therefore, hardly reach rigid conclusions. 

Lastly it appears that, pre-literate in areas where the history student is faced with an absence of the historian's usual materials, the analysis of institutions is probably one of the most fruitful approaches.