Two things to note: Firstly, both searches demonstrate a nice positive upward trend in articles mentioning the respective search terms. Secondly, the charts clearly show that the trend in mentions of 'Engagement' predates the trend in 'Social Media' by almost a decade. (N.B. The search for "engagement" is actually the aggregated search on over 60 bigrams like "engaging audiences", "emotional engagement" and "engages with")

1. AGGREGATE MONTHLY MENTIONS IN 'BRAND REPUBLIC' ARCHIVE
"ENGAGEMENT" TREND "SOCIAL MEDIA" TREND
150
100
50
0
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013