In the fall of 1986, White quit the band in order to form the short-lived Khymera with Juggernaut drummer Bobby Jarzombek and former Karion bassist Pete Perez before joining Don Dokken for the Up from the Ashes album in 1990. With Watchtower's future now in doubt, Doug Keyser auditioned (but failed) for Metallica following the death of bassist Cliff Burton.
Jason McMaster was approached by Texas based Pantera who were looking for a new vocalist. That venture didn't turn out, but he eventually left in 1988 when he was signed to a major label for his side project Onyxx, later renamed Dangerous Toys. Their self-titled CBS debut came close to making gold status.
White's replacement was Ron Jarzombek (ex-S.A.Slayer, while McMaster was replaced by Mike Soliz (ex-Militia/ex-Assalant), but eventually was later replaced by former Hades vocalist Alan Tecchio. Now signed to 'Noise Records', the act flew to Berlin, Germany in the summer of 1989 to record their second album, Control And Resistance, released in 1990.
Soon after embarking on their first European tour and follow-up, US tour, Ron Jarzombek developed severe hand problems which required multiple surgeries, effectively putting Watchtower on ice indefinitely, as was it's proposed third album, Mathematics.
In 1999, original Watchtower members McMaster, Keyser and Colaluca reunited, along with Jarzombek, to record a cover of Accept's Run If You Can for A Tribute to Accept - Vol. 1 on 'Nuclear Blast Records'. The band also began work on the long dormant Mathematics album, but progress stalled once again.
In 2002, 'Monster Record's issued Demonstrations in Chaos, a compilation featuring early recordings, demos, and unreleased tracks, including almost the complete original Energetic Disassembly recordings and the 1987 demos with Ron Jarzombek.
The band returned to Europe once more in 2004 to headline the 'Headway Festival' in Amstelveen, Holland. Ron Jarzombek also released the second Spastic Ink album, Ink Compatible, with guest contributions by Watchtower band mates Doug Keyser and Jason McMaster who contributed lead vocals on five songs. In the fall of 2004, 'Monster Records', now 'Monster Underground', re-issued Energetic Disassembly on CD for the first time ever in the United States. The original CD re-issue came 1993, by Germany's 'Institute of Art' label.
On April 9, 2010, the band released a preliminary mix of The Size of Matter from their still forthcoming album Mathematics as a digital-only single featuring Ron Jarzombek, Doug Keyser, and Rick Colaluca, along with a returning Alan Tecchio on vocals. Tecchio then replaced Jason McMaster for the second time. The folllow up EP, Concepts of Math: Book One, (2016) featured the previously released tracks from a set of digital only EP's released during 2015 (Arguments Against Design, M-Theory Overture, Technology Inaction), as well as the new track Mathematica Calculis.