Sub CreateList()
Dim wks As Worksheet
Dim wkb As Workbook
Dim newsheet As Worksheet
Dim lastRow As Long
Set wkb = ThisWorkbook
Set newsheet = wkb.Worksheets.Add
newsheet.Name = "Suppliers"
For Each wks In Worksheets
lastRow = wks.Cells(Rows.Count, 1).End(xlUp).Row
Debug.Print lastRow
Range("D1:D" & lastRow).Copy Destination:=newsheet.Range("A1:A" & lastRow)
Next wks
End Sub

Sub CreateList()
    Dim wks As Worksheet
    Dim wkb As Workbook
    Dim newsheet As Worksheet
    Dim lastRow As Long
    Dim newRow As Long
    Set wkb = ThisWorkbook
    Set newsheet = wkb.Worksheets.Add
    newsheet.Name = "Suppliers"
    ' Start in row 1 on new sheet
    newRow = 1
    For Each wks In Worksheets
        If wks.Name <> newsheet.Name Then
            lastRow = wks.Range("D" & wks.Rows.Count).End(xlUp).Row
            wks.Range("D1:D" & lastRow).Copy _
                Destination:=newsheet.Range("A" & newRow)
            ' Add the number of copied rows to newRow
            newRow = newRow + lastRow
        End If
    Next wks
End Sub