Even back then, extending Brussels’ territory was not a new idea. Adolphe Max was not the only one, in the 1910s, to think about an expansion plan and municipal merger. Like his competitors, he sought inspiration from the broad outlines of previous projects that never saw the light of day due to the vagaries of parliamentary life. Although none of these projects had succeeded due to the outbreak of the First World War, the end of hostilities quickly revived the interest of elected officials in Brussels for the extension of their jurisdiction.

As early as 1919, they sought to fulfil the ambitions of their predecessors, citing reasons as diverse as they were varied: the need for the City to develop its maritime facilities, to find constructable land and to retain those inhabitants in search of more space; the desire of the various municipal authorities to unify their services in order to simplify administrative life (civil status, hospitals, fire-fighters, etc.); the government's wish to pursue the development of the City in keeping with that of a large European capital, etc. Other reasons, resulting from less admirable political aspirations, could also be taken into account, such as the desire to carve out a liberal and/or Catholic electorate which would be able to counterbalance the socialist tendency of Brussels centre.

Whatever the reason, the political and economic stakes of the expansion of the Capital eventually prevailed over the desiderata of the suburbs’ inhabitants: not only were they not consulted about their annexation (by referendum or popular consultation, for example), but their representatives, who originally had not been informed of Brussels’ plans, loudly proclaimed their opposition to the bill. Indeed, as early as 1919, faced with the scale of the new expansion plans, the suburban municipalities took the initiative to set up an Inter-municipal Commission tasked with studying the various plans for their merger and how they were to be carried out, in particular those established by the mayor of the City of Brussels’ proposal.

While unifying services appeared to many as the appropriate solution to the problem of administrative complexity, the delegates of the agglomeration’s various municipalities, on the other hand, expressed their strong opposition to the "pure and simple annexation" of municipal territories such as was recommended by Adolphe Max. The Brussels administration, invited to take part in the debates, did not deem their representation at these meetings necessary - with the exception of a single meeting during which Adolphe Max expressed his disinterest in the Inter-municipal Commission’s project and instructed the representatives present to vote on his bill. The deliberations of the Inter-municipal Commission, resuming without the representatives from Brussels, consequently led to the drafting of an alternative bill retaining the autonomy of the municipalities (the “De Bue” bill which would be tabled on 15th April 1920), as well as a unanimous vote by the Municipal Councils inviting the Chambers to “vigorously” reject Adolphe Max's proposal.

At the same time as these debates, the Senate had nevertheless set up a Government Commission to examine the problem of the unification of the territories surrounding maritime facilities. After two sessions, this Commission voted on a resolution calling for the annexation to the City of Brussels of the municipalities of Molenbeek, Laeken, Jette, Koekelberg, Ganshoren, Neder-Over-Heembeek, Berchem, Haren and part of Schaerbeek - and this, in spite of strong protests from the municipal representatives, in particular those of Mr. Coelst (representative of Laeken) and of Mr. Brion (mayor of Neder-Over-Heembeek). This government resolution is what inspired Adolphe Max to draft the “urgent” bill which he tabled on 24th February 1920 in the Chamber of Representatives, undoubtedly in order to get ahead of the competing proposals ("De Bue" and "Hallet” bills). The mayor of the City of Brussels had however gone beyond the wishes of the Government Commission, since he had extended the annexation to several other municipalities and erased the “special” nature related to the extension of maritime facilities.

The Chamber of Representatives and the Senate began examining the question of the expansion of Brussels on 10th March 1921. In order to assemble the required majority, the “Max” bill was reduced to the annexation of the municipalities of Laeken, Neder-Over-Heembeek and Haren, as well as small areas of land located in Molenbeek and Schaerbeek. During the deliberations, some elected representatives reminded participants of the unfavourable opinion that the Municipal Councils of these five suburbs had issued on this subject, as well as certain groups of residents of Laeken who had written letters expressing their surprise at having never been consulted about their annexation to the City of Brussels (documents sent by post to Adolphe Max's office between February and May 1921). In session on 17th March, the Senate even recorded a petition from the Municipal Council of Schaerbeek reiterating its previous protests regarding the total or partial annexation of municipalities in the agglomeration to the City of Brussels. Conversely, some of the parliamentarians affirmed on several occasions during the discussions that "the populations concerned had unanimously rallied to the bill or at least that the representatives who were qualified to speak on their behalf had endorsed the project".

In spite of the strong protests which it had sparked in the main interested parties, the “Max” bill was passed in the House on 17th March 1921, before being approved by the Senate the following 22nd March. The attachment of the municipalities of Laeken, Haren and Neder-Over-Heembeek to the City of Brussels was therefore more akin to an "annexation" than a simple merger. This was certainly not the will of those living in these suburbs, but rather that of elected officials in Brussels.