By 1890, however, Vaughan had recognized that Slattery’s memorandum applied to Europe as well as America.  So, he assigned two priests to start European expansions.  Fr. John Aelen was assigned to establish a Society seminary at Roosendaal in the Netherlands.  Fr. Joseph Kleinschneider was given a similar task in Brixen, then in Austrian Tyrol.  As the new Roosendaal and Brixen candidates began to filter through the system, and incidentally, training of lay brothers expanded, extra accommodation at Mill Hill became necessary.  This led to the building in 1896 of what is now known as the Superiors’ Wing.  These arrangements meant that St. Joseph’s Mill hill concentrated on theological formation.  The Dutch and Austrian institutions catered for Philosophy.  It brought too a major alteration in student training.  British and Irish students were required to study philosophy in the Netherlands.  This insured that each candidate for the Society, before being accepted, had had experience of living and working in a culture foreign to his own.   It also sifted out those candidates who lacked the ability to cope with foreign languages.

After the First World War, a number of new pressures began to be exerted on the college.  The church introduced a programme of draconian reforms of discipline and teaching in seminaries in response to Modernism. Studies were extended from five to six years.  On the political front, German missionaries in French and British colonial territories were expelled en masse.   The missionaries from other lands had to pick up the slack.  This means a sudden increase in the obligations of societies like the Mill Hill Missionaries.

The extension of the seminary course by one year, and the changes brought earlier in respect of the Roosendaal/Mill Hill cooperation meant that St. Joseph’s College required 25% more accommodation for students. To meet this need an extra wing, the C-Wing, was completed in 1926.  Between 1918 and 1924, recruitment to the Mill Hill Missionaries was at an all-time low.  The 1924 General Chapter addressed this problem and chose to respond to it be beginning recruitment at an earlier age.  Thus, in the 1920s and 1930s, seven more minor seminaries were established as recruitment grounds.  The effects of this approach were such that the C-Wing was hardly opened when further increase in accommodation was demanded.   A new wing, known as the D-Wing, was ready for occupation in 1932.  It gave the college the capacity to handle up to 150 students.  Recruitment between 1930 and 1965 justified this accommodation.  The annual ordination classes seldom numbered less than 25, and in 1938, 46 new priests were ordained.  Membership of the Mill Hill Missionaries expanded to more than 1200 persons.

The training of the lay brothers had, by this time, been moved out of Mill Hill to Vrijland in the Netherlands.  This meant that the college returned to its original function of being strictly a training ground for missionary priests.  Another political factor of the 1920s brought an important change in the training programme.  This came as a result of a number of reports commissioned by the Colonial Office.  The most important of these, in respect of the Mill Hill Missionaries, were the Phelpes-Stokes report on East Africa and the Simon Report on India.  These reports recommended that the colonial government place greater stress on education.   It was also recommended that there should be a partnership with the missionaries in achieving this.  To take advantage o this, many young priests, after ordination, were not sent straight away to the missions.  Instead they went on to university to gain secular degrees.  Thus a steady stream of Mill Hill priests attended the Universities of Cambridge, Liverpool, Durham, Glasgow, Rome and Nijmegen.  During this period, life at St. Joseph’s was steady, but not very eventful.