what s fundamental difference between vadagalai and thengalai acharya sampradayam

adiyen ramanuja dasan…….what s fundamental difference between vadagalai and thengalai acharya sampradayam…….many say swami desikan also lived as part of thenacharya sampradayam as per srirangam “koilozhugu”, i want unite all srivaishnavas under single roof , to completely the differencs of vadagalaiand thengalai, only withblessings of periya perumal and swami ranmanujar , i m aspiring to start !!!